Slow cooker Mongolian beef is a Chinese-American takeout-style dish of tender beef strips coated in a glossy, sweet-and-savoury soy, garlic and ginger sauce. This home version uses familiar UK ingredients and a slow cooker for hands-off cooking; serve it over rice with spring onions for an easy, satisfying meal.
Ingredients
- 900 g (2 lb) flank steak or sirloin steak, trimmed and fully thawed
- 2 tbsp (16 g) UK cornflour, for coating the beef
- ½ cup (120 ml) reduced-salt soy sauce
- ⅓ cup (80 ml) water
- ½ cup packed (100 g) light brown sugar
- 1 tbsp (15 ml) hoisin sauce
- 4 garlic cloves (about 12 g), finely chopped or grated
- 1 tbsp (6 g) finely grated fresh ginger
- 1 tsp (5 ml) sesame oil
- ¼ tsp (0.5 g) chilli flakes, or to taste
- 2 tbsp (16 g) cornflour, for thickening the sauce
- 2 tbsp (30 ml) cold water, to mix with the thickening cornflour
- 4 spring onions (about 40 g), thinly sliced
- 1 tbsp (9 g) sesame seeds, to finish
Instructions
- Prepare the beef. Slice the steak across the grain into strips about 1 cm (⅜ inch) thick and 5–7 cm (2–3 inches) long. Cutting across the visible muscle fibres helps keep the pieces pleasant to eat. Pat the strips dry, put them in a bowl and toss with the 2 tablespoons of cornflour until lightly coated. Separate any clumps so the pieces do not stick together.
- Mix the sauce. In a jug or bowl, whisk together the soy sauce, water, brown sugar, hoisin, garlic, ginger, sesame oil and chilli flakes. Stir until the sugar is mostly dissolved. Reduced-salt soy sauce helps keep the finished sauce from becoming overly salty as it cooks down; if using regular soy sauce, do not add extra salt.
- Load the slow cooker. Put the coated beef in the slow-cooker pot and pour the sauce over it. Stir gently so the strips are covered. Cover with the lid and cook on LOW for 3 hours 30 minutes. Keep the lid closed as much as possible: each lift lets heat escape and can lengthen the cooking time. Do not put frozen beef in the slow cooker; thaw it safely in the fridge first.
- Check the beef. At the end of the cooking time, check the largest strip with a food thermometer, inserting a thin probe from the side if possible. The USDA FSIS safe minimum for whole cuts of beef is 145°F (63°C), followed by a 3-minute rest. The strips should also be tender when pierced; if they are still firm, continue cooking and check again after 15 minutes. Slow cookers vary, so tenderness and temperature matter more than the clock alone.
- Thicken the sauce. Stir the remaining 2 tablespoons of cornflour with 2 tablespoons of cold water until smooth. Stir this slurry into the hot sauce, cover and cook on HIGH for 15 minutes, until the sauce looks glossy and lightly thickened. Switch off the cooker and leave the beef to rest in the hot sauce for 3 minutes. Stir in most of the spring onions, then scatter the rest and the sesame seeds over the top.
Tips
- Choose a suitable cut. Flank steak gives a familiar, beefy texture, while sirloin is usually leaner and can cook a little faster. Slice either cut across the grain and keep the strips a similar thickness so they cook evenly. Avoid very lean, thin frying steak if your cooker runs hot, as it can become dry before the sauce has time to develop.
- Know your cornflour. In UK recipes, cornflour means the fine white starch also called cornstarch in the US, not coarse maize meal or yellow cornmeal. It coats the beef and thickens the sauce. If you only have arrowroot, use the same amount for the slurry and stir it in near the end; the sauce may turn slightly clearer and can thin if boiled hard.
- Balance the sauce to your taste. For a less sweet result, start with ⅓ cup (65 g) brown sugar and add a little more after cooking if needed. For extra heat, add more chilli flakes at the table. Avoid pouring in extra soy sauce early: the slow cooker does not reduce liquid like an uncovered pan, so the flavour can become much saltier than expected.
- Use the slurry correctly. Mix cornflour with cold water before adding it to the hot sauce; sprinkling dry starch straight into the cooker can leave lumps. If the sauce is still thinner than you like after 15 minutes on HIGH, mix another teaspoon of cornflour with a teaspoon of cold water and cook for a further 5–10 minutes.
Serving Suggestions
Serve the beef and plenty of sauce over steamed long-grain rice, jasmine rice or basmati rice. For four portions, allow about 1½ cups (285 g) uncooked rice and cook it separately according to its packet directions. The rice is not included in the recipe timings. Spoon the beef on top just before serving so the rice can catch the savoury-sweet sauce, then add spring onions and sesame seeds for freshness and a little crunch.
For vegetables, offer steamed broccoli, pak choi, tenderstem broccoli or green beans alongside the beef. Their clean, slightly bitter flavour balances the rich sauce. You can also serve a simple cucumber salad or lightly dressed shredded cabbage for a crisp contrast. If you want a lighter base, use cauliflower rice, or serve the beef in lettuce cups; the latter is messier, so keep extra napkins nearby.
Variations
Make it spicier: Increase the chilli flakes to ½ teaspoon or serve sliced fresh chilli separately, which lets everyone choose their own heat level. A little chilli sauce can work too, but taste before adding it because some varieties are quite salty or sweet.
Add vegetables: Stir in sliced red pepper or trimmed green beans for the final 30–45 minutes of cooking so they soften without disappearing into the sauce. For broccoli, steam it separately and fold it through just before serving; cooking florets for the full slow-cooker time tends to make them too soft. Adding vegetables can also dilute the sauce slightly, so check its consistency after thickening.
Use a different cut or sauce ingredient: Thinly sliced skirt steak can replace flank steak, though cooking time may vary with thickness. If hoisin is unavailable, use 1 tablespoon (15 ml) oyster sauce plus 1 teaspoon (5 ml) extra brown sugar. The flavour will be less rounded and slightly less sweet than with hoisin. For a gluten-free version, use certified gluten-free tamari and check the hoisin label; not every brand is gluten-free.
Storage and Reheating
Transfer leftover beef and sauce to a shallow, covered container and refrigerate within 2 hours of cooking. It keeps for 3–4 days in the fridge. Store rice separately where possible, because keeping it apart makes it easier to cool promptly and reheat evenly. If the sauce sets or thickens in the fridge, that is normal; it will loosen as it warms.
Reheat only the portion you need, either in a saucepan over a low-to-medium heat or in the microwave, stirring partway through. Add a splash of water if the sauce is too thick. Heat until steaming throughout and check that leftovers reach 165°F (74°C), the USDA FSIS reheating temperature. Do not reheat the same portion repeatedly. You can freeze the cooled beef and sauce for up to 2–3 months for best quality; thaw overnight in the fridge and reheat as above.
Frequently Asked Questions
Can I cook Mongolian beef on HIGH instead?
This recipe is timed for LOW, which gives the beef time to become tender without rushing the sauce. HIGH settings vary considerably between slow cookers, and thin strips can overcook if left too long. If you need to use HIGH, start checking the beef after about 1 hour 45 minutes and check every 15 minutes thereafter. Use the thermometer and tenderness checks in the instructions rather than assuming every cooker will finish at the same time.
Do I need to brown the beef first?
No. Browning is optional, and this recipe skips it to keep preparation straightforward. Searing can add a deeper roasted flavour, but it takes extra time and is not needed for the beef to cook safely in the sauce. If you do sear it, work in batches in a hot pan so the beef browns rather than steams, then transfer the browned strips and any pan juices to the slow cooker.
Why is my sauce thin?
Slow cookers trap moisture, so the sauce will not reduce in the same way it would in an uncovered frying pan. Make sure the cornflour is mixed into a smooth cold-water slurry and give it the full 15 minutes on HIGH with the lid on. If you added extra vegetables or liquid, it may need a little more thickener. Add it gradually, because too much cornflour can make the sauce stodgy.
Can I prepare the ingredients ahead?
Yes. You can slice the beef and mix the sauce up to a day ahead, keeping each in a separate covered container in the fridge. Toss the beef in cornflour shortly before adding it to the cooker; coating it far in advance can make the starch damp and clumpy. Keep raw beef separate from ready-to-eat foods, and do not leave the assembled slow-cooker pot sitting at room temperature while you wait to start cooking.
Is Mongolian beef actually from Mongolia?
The restaurant-style dish commonly called Mongolian beef is associated with Chinese-American cooking rather than being a traditional Mongolian dish. Recipes and sauces differ between restaurants and home cooks. This slow-cooker version follows the familiar sweet-savoury profile of beef, soy, garlic and ginger, but it is a convenient home adaptation rather than a claim to represent one definitive regional recipe.
Related
- Mongolian Pork Recipe, Chinese-Style and Easy to Make
- Mongolian Beef Recipe with a Glossy Wok Sauce
- Mongolian Beef Sauce Recipe for Glossy, Savory Beef
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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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