Mongolian beef with onions is a Chinese-American restaurant-style stir-fry of tender beef strips, soft-edged onions, and a glossy soy, garlic, and brown sugar sauce. It comes together quickly in a hot pan, and cooking the beef in batches helps it brown instead of steam; versions vary, but this one keeps the sauce balanced and lets the onions stay noticeable.
Ingredients
- 1½ lb flank steak (680 g), trimmed and sliced thinly across the grain
- 2 medium yellow onions (about 300 g), peeled and cut into ½-inch (1.3 cm) wedges
- ⅓ cup cornstarch (40 g), for coating the beef
- 3 tablespoons neutral oil (45 ml), such as canola or vegetable oil, divided
- ⅓ cup reduced-sodium soy sauce (80 ml)
- ⅓ cup water (80 ml)
- ¼ cup packed light brown sugar (55 g)
- 3 garlic cloves (about 9 g), finely minced
- 1 tablespoon finely grated fresh ginger (about 6 g)
- ¼ teaspoon red pepper flakes (about 0.5 g), or more to taste
- 1 tablespoon cornstarch (8 g), for thickening the sauce
- 2 tablespoons cold water (30 ml), for the sauce slurry
- 1 teaspoon toasted sesame oil (5 ml), optional
- 3 scallions (about 30 g), thinly sliced, for serving
- 1 teaspoon sesame seeds (3 g), optional, for serving
Instructions
- Prepare the beef and onions. Pat the steak dry so the coating sticks and the meat can brown. Slice it across the grain into strips about ¼ inch (6 mm) thick; cutting across the visible muscle fibers makes each bite easier to chew. Separate the onion wedges into pieces that will cook evenly. If the steak feels soft and difficult to slice, chill it in the freezer for 15 to 20 minutes before cutting; that optional wait is not included in the recipe timing.
- Mix the sauce and coat the beef. In a bowl, stir together the soy sauce, ⅓ cup water, brown sugar, garlic, ginger, and red pepper flakes until the sugar is mostly dissolved. In a small separate cup, whisk the 1 tablespoon cornstarch with 2 tablespoons cold water until smooth. Toss the sliced steak with the ⅓ cup cornstarch in a large bowl, separating pieces so there are no thick, pasty clumps. Let excess starch fall back into the bowl; an even, light coating is what you want.
- Brown the beef in batches. Heat a large wok or heavy skillet over medium-high to high heat. Add 1 tablespoon oil and swirl to coat the pan. When the oil shimmers, add half the beef in a single layer, leaving space between pieces. Cook for about 2 to 3 minutes, turning once, until browned and cooked through; transfer to a clean plate. Add another tablespoon oil and repeat with the remaining beef. Avoid crowding the pan, since packed strips release moisture and turn pale rather than sear. Check the thickest strips with an instant-read thermometer; USDA FSIS lists 145°F (63°C) with a 3-minute rest as the safe minimum for whole cuts of beef. Rest the cooked strips on the plate for 3 minutes while you cook the onions.
- Cook the onions. Add the remaining 1 tablespoon oil to the pan if it looks dry. Add the onions and stir-fry for 3 to 4 minutes, moving them often, until they soften at the edges but still have a little bite. If browned bits are sticking, add a tablespoon of water and scrape them up; they add flavor to the sauce. Keep the heat high enough to cook the onions briskly, but lower it if the garlic residue in the pan begins to darken.
- Thicken the sauce and finish. Pour the soy mixture into the pan and bring it to a steady simmer, stirring to dissolve any browned bits. Whisk the cornstarch slurry again, then stir it into the bubbling sauce. Cook for about 1 minute, until glossy and lightly thickened. Add the rested beef and any juices from its plate, then toss for about 1 minute so the sauce coats the strips and onions. Turn off the heat and stir in the sesame oil, if using. Scatter over the scallions and sesame seeds and serve promptly.
Tips
- Slice across the grain. Look for the long lines running through the steak and cut across them, not parallel. If you slice with the grain, even a quick-cooking cut can seem chewy. Keep the strips similar in thickness so the smaller pieces do not overcook while thicker ones finish.
- Use a hot, roomy pan. A wok is convenient, but a wide stainless-steel or cast-iron skillet works well. If your pan is small, cook the beef in three batches rather than crowding it. Let the pan regain heat between batches and add a little oil only if it needs it.
- Adjust the sauce thoughtfully. Reduced-sodium soy sauce gives you more control over salt. If using regular soy sauce, start with ¼ cup (60 ml) and add a splash more at the end if needed. Brown sugar provides the familiar sweet-savory flavor; use a little less for a less sweet sauce, but do not omit it entirely or the sauce will taste sharper and reduce differently.
- Choose practical substitutes. Sirloin can stand in for flank steak; slice it thinly across the grain and avoid overcooking. If fresh ginger is unavailable, use 1 teaspoon ground ginger (about 2 g), though its flavor is warmer and less bright. Tamari can replace soy sauce in the same amount, but check its salt level because brands differ.
Serving Suggestions
Serve the beef and onions over steamed jasmine rice, brown rice, or plain long-grain rice so the grains catch the glossy sauce. For a noodle dinner, toss the stir-fry with cooked wheat noodles or serve it alongside them; keep a little noodle water nearby if you want to loosen the sauce before tossing. The sauce is concentrated, so a simple base works better than a heavily seasoned one.
Add a green vegetable to round out the plate. Steamed broccoli, sautéed bok choy, snap peas, or quickly blanched green beans all work without competing with the sweet-savory sauce. For a family-style meal, place rice, beef, vegetables, scallions, and sesame seeds in separate bowls so everyone can assemble a portion. Offer extra red pepper flakes at the table rather than making the whole pan very spicy.
Variations
More onion-forward: Use three medium onions, about 450 g total, and cook them in two batches if the skillet is not wide. They will release more moisture and take a little longer to brown, so keep stirring and let the liquid evaporate before adding the sauce. Sweet yellow onions work particularly well; red onions are also fine but stay a little firmer and give the finished dish a sharper edge.
Less sweet or more heat: Reduce the brown sugar to 2 tablespoons (about 28 g) for a more savory sauce. For a hotter version, increase the red pepper flakes to ½ teaspoon or finish with sliced fresh chile. Add heat gradually: the sauce concentrates as it simmers, and it is easier to add more at the table than to correct an overly hot pan.
Add vegetables: Bell pepper strips, sliced mushrooms, or broccoli florets can join the onions. Cook firm vegetables until nearly tender before adding the sauce; broccoli may need a brief steam or blanch first. Extra vegetables release moisture, so cook them in batches and allow excess water to evaporate. The dish will have a lighter coating of sauce unless you increase the sauce ingredients proportionally.
Gluten-free option: Use tamari or a certified gluten-free soy sauce, and check that the cornstarch and any other packaged ingredients are labeled gluten-free if that matters for your meal. The flavor remains close, although tamari may taste deeper or saltier depending on the product. Do not substitute ordinary flour for the cornstarch in the coating; it browns differently and will not give the same light crust.
Storage and Reheating
Refrigerate leftovers within 2 hours of cooking in a shallow, airtight container. The beef and onions keep for 3 to 4 days in the refrigerator. Store rice separately when possible so it is easier to cool and reheat evenly. For longer storage, freeze the cooled stir-fry in a freezer-safe container for up to 2 months for best texture; thaw it overnight in the refrigerator. The onions soften more after freezing, but the dish remains useful for a quick meal.
Reheat only the portion you plan to eat. Warm it in a skillet over medium heat with 1 to 2 tablespoons (15 to 30 ml) of water, stirring until hot throughout; the added water loosens the sauce as it heats. A microwave also works: cover loosely, heat in short intervals, and stir between them. USDA FSIS recommends reheating leftovers to 165°F (74°C); check the center with a food thermometer rather than relying only on the sauce bubbling. Avoid repeated cooling and reheating, which can dry out the beef.
Frequently Asked Questions
Is Mongolian beef actually from Mongolia?
The name can be misleading. Mongolian beef as commonly served in North American restaurants is a Chinese-American style dish, not a claim that this particular soy-and-sugar stir-fry represents traditional Mongolian cooking. Recipes vary between restaurants and home cooks; some use scallions, some include onions, and the sweetness and heat levels differ. This version uses onion wedges so they remain a clear part of the meal.
What is the best cut of beef for this recipe?
Flank steak is a good choice because it is easy to slice across the grain and cooks quickly. Sirloin is a practical alternative, while skirt steak also works if trimmed and sliced across its fibers. Whichever cut you choose, keep the strips thin and reasonably even. Very lean, thin pieces can overcook quickly, so use a hot pan and cook in batches rather than leaving the meat in the skillet while the sauce reduces.
Can I make the sauce ahead of time?
Yes. Stir together the soy sauce, water, brown sugar, garlic, ginger, and pepper flakes up to 2 days ahead and refrigerate in a covered container. Keep the cornstarch slurry separate and mix it just before using, because cornstarch settles in water. For the best texture, slice and coat the beef shortly before cooking; coating it far ahead can make the starch damp and patchy.
How do I keep the beef from turning tough?
Slice across the grain, do not overcrowd the skillet, and remove each batch as soon as it is cooked to the safe temperature. Thin strips cook fast, so avoid leaving them in the pan while you prepare the onions. Returning the beef to the sauce for only about a minute is enough to warm and coat it. A lower-quality or thicker cut may need slightly different timing, so use a thermometer and the appearance of the thickest strip as guides.
Can I make this without a wok?
Absolutely. Use the widest heavy skillet you have so the beef can sit in a single layer and the sauce can reduce without spilling. A wok heats differently, but the key is high heat, small batches, and frequent movement once the onions go in. If your burner is not powerful, allow extra time for the pan to heat between batches rather than putting all the beef in at once.
Why is my sauce too thin or too thick?
A thin sauce may need another brief simmer after the cornstarch slurry goes in; make sure it reaches a simmer so the starch thickens. If it becomes too thick, stir in water a tablespoon (15 ml) at a time until it coats the beef without clinging in a heavy layer. The sauce also thickens as it cools, so judge its consistency while hot and serve soon after tossing the beef through it.
Related
- Mongolian Beef Recipe with a Lighter Skillet Sauce
- Mongolian Lamb Recipe: Chinese-Style Stir-Fry with Ginger and Garlic
- Slow Cooker Mongolian Beef with Kimchi
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Safety notes: safe minimum internal temperatures from USDA FSIS; raw and undercooked fish guidance from the U.S. FDA. Food safety notes
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