Condensed French Onion Soup: A Homemade Concentrate

Condensed French onion soup is a deeply savory, reduced version of the French classic, made with slowly browned onions, broth, thyme, and a little flour for body. Its concentrated flavor makes it useful as a quick bowl of soup when diluted, or as a flavorful base for casseroles and other dishes; French onion soup has plenty of regional and family variations.

Ingredients

3 lb yellow onions (1.36 kg), peeled, halved, and thinly sliced
3 tbsp unsalted butter (42 g)
1 tbsp olive oil (15 ml)
2 garlic cloves (about 6 g), finely chopped
2 tbsp all-purpose flour (16 g)
1/2 cup dry white wine (120 ml), optional
6 cups beef broth (1.42 L), preferably low-sodium
1 tsp fresh thyme leaves (about 1 g), or 1/2 tsp dried thyme (about 0.5 g)
1 bay leaf
1 tbsp Worcestershire sauce (15 ml)
1 tsp fine salt (6 g), plus more to taste
1/2 tsp freshly ground black pepper (about 1 g)

Yellow onions are a dependable choice because they turn sweet and mellow as they cook. White onions work too, though their flavor can be sharper; sweet onions become soft quickly and may taste noticeably sweeter in the finished concentrate. Beef broth gives the most familiar, rounded flavor. A good vegetable broth is a practical substitute, but the result will be lighter and will not have the same beefy depth. If your broth is salty, start with half the listed salt and adjust at the end.

The wine is optional, but it adds acidity that balances the onions and helps lift the browned bits from the pan. Use dry white wine rather than a sweet variety. For an alcohol-free version, replace it with an equal amount of broth and add 1 teaspoon (5 ml) cider vinegar or lemon juice near the end; the flavor will be a little brighter and less wine-like. Worcestershire sauce adds savory depth. A vegetarian Worcestershire-style sauce can replace it if you are using vegetable broth.

Instructions

Peel and thinly slice the onions, aiming for pieces of similar thickness so they soften evenly. Measure the remaining ingredients before you start cooking. A wide, heavy-bottomed pot or Dutch oven gives the onions room to brown; a narrow pot crowds them and encourages steaming instead.
Set the pot over medium heat and add the butter and olive oil. When the butter has melted, add the onions and salt. Stir to coat, then cook uncovered for 40 minutes, stirring every few minutes and scraping the bottom when color builds there. The onions will first soften and release liquid, then shrink and gradually turn golden brown. If the bottom begins to scorch, lower the heat and add a tablespoon of water to loosen the browned bits. The goal is deep golden color, not blackened edges.
Stir in the garlic and cook for 1 minute, just until fragrant. Add the flour and stir continuously for another minute so it coats the onions and loses its raw, dusty smell. The small amount of flour gives the concentrate a fuller texture when diluted; it should not make the soup paste-like.
Pour in the wine, if using, and scrape the bottom of the pot to release the flavorful browned bits. Let it bubble for 3 minutes. Add the broth, thyme, bay leaf, Worcestershire sauce, and black pepper. Stir well, bring the mixture to a gentle simmer, and cook uncovered for 26 minutes. Stir occasionally, especially toward the end, as the soup thickens. It should be savory and noticeably more concentrated than ready-to-serve soup, with the onions still tender rather than dry.
Remove the bay leaf and taste. Add more salt or pepper only if needed, since broth and Worcestershire vary in saltiness. Let the concentrate cool in the pot for about 10 minutes before portioning. It will thicken a little more as it cools. The recipe makes approximately 6 cups (1.4 L), though the exact yield depends on how much moisture the onions release and how rapidly the broth reduces.
To serve as soup, combine 1 cup (240 ml) concentrate with 1 cup (240 ml) hot water or broth per person, then heat gently until steaming. Use water for a balanced, classic soup or broth for a richer bowl. Taste after diluting and adjust the seasoning. For a thicker bowl, begin with 3/4 cup (180 ml) liquid per cup of concentrate and add more to taste.

Tips

Give the onions time. Their color and sweetness develop gradually, and turning the heat high to hurry them can burn the edges while leaving the centers pale. If the onions are browning too fast, reduce the heat; if they are releasing liquid and staying pale, keep the pot uncovered and let the moisture evaporate.
Use a wide pot and stir often enough to prevent scorching. A few brown bits on the bottom are useful flavor, but black patches taste bitter. Loosen light browning with a splash of water, wine, or broth rather than scraping burnt residue into the soup.
Choose low-sodium broth when possible. Reduction concentrates salt as well as flavor, so heavily salted broth can make the finished soup difficult to correct. Season at the end, and remember that cheese or salty bread toppings will add more salt when you serve it.
For a gluten-free batch, omit the flour and simmer until the broth is reduced to your preferred strength. The concentrate will be thinner, but it will still taste rich. To add body without wheat, whisk 1 teaspoon (3 g) cornstarch with 1 tablespoon (15 ml) cold water and stir it into the simmering soup during the final few minutes.

Serving Suggestions

Dilute the concentrate with hot water or broth for a quick bowl, then finish with black pepper and a few thyme leaves. For a French onion-style topping, ladle the diluted soup into heatproof bowls, place a toasted baguette slice on each, and add grated Gruyère or Swiss cheese. Broil until the cheese is melted and bubbling, keeping the bowls under close watch and using broiler-safe dishes. The bread and cheese are serving additions rather than part of the concentrate, so prepare only as much as you plan to eat.

The concentrate is also useful beyond a bowl of soup. Stir a few spoonfuls into pan sauce, gravy, or a pot of lentils for a sweet-savory onion note. It can flavor rice or mashed potatoes, or serve as a starting point for a casserole sauce when loosened with broth or milk. Because it is seasoned and reduced, add it gradually and taste before adding extra salt. For a simple weeknight meal, serve a diluted bowl with a green salad or a plain cheese sandwich.

Variations

For a vegetarian version, use vegetable broth and vegetarian Worcestershire sauce. The soup will be less robust than the beef-broth version, so consider adding 1 teaspoon (5 ml) soy sauce or tamari with the broth for extra savory depth. Start with a small amount, since these seasonings can be salty. A splash of balsamic vinegar at the end can add a rounded tang, but use it sparingly so it does not overpower the onions.

For a deeper, darker flavor, replace the white wine with 1/2 cup (120 ml) dry red wine. It will give the concentrate a fuller, more pronounced wine character. You can also use all yellow onions or replace up to one-third of them with red onions; red onions make the finished soup a little sweeter and darker in color. If fresh thyme is unavailable, dried thyme works as listed. Avoid adding extra sugar to force browning: patiently cooked onions provide plenty of sweetness on their own.

To make a batch without flour, simply leave it out and reduce the broth a little further if you want a stronger concentrate. For a richer finish, stir 1 tablespoon (14 g) of butter into the warm soup after cooking. This is best for soup you plan to eat right away; the added butter can make a frozen batch slightly less smooth after thawing.

Storage and Reheating

Cool the soup promptly and refrigerate it within 2 hours of cooking. Store it in a covered, shallow container so it chills efficiently. The concentrate keeps for 3 to 4 days in the refrigerator. It may thicken as it sits; that is normal, and you can loosen it with a little water or broth when reheating.

For longer storage, freeze the cooled concentrate in airtight containers or freezer-safe portions for up to 3 months for best quality. Leave a little room at the top of each container for expansion, and label it with the date. Thaw overnight in the refrigerator or warm it gently from frozen in a saucepan with a splash of water, stirring as it loosens. Avoid leaving soup at room temperature for extended periods.

Reheat only the amount you plan to serve, either in a saucepan over medium-low heat or in the microwave in a covered, microwave-safe container, stirring partway through. Reheat leftovers to 165°F (74°C), checking with a food thermometer, and bring diluted soup to a steaming temperature before serving. If the soup has been diluted already, it can be stored and reheated in the same way; the concentrate is simply easier to portion before adding liquid.

Frequently Asked Questions

What does condensed French onion soup mean?

Here, condensed means the soup has been reduced and seasoned more strongly than a ready-to-eat bowl, so you add liquid before serving. This homemade version is an onion-rich concentrate, not an exact copy of any canned product. Its thickness and seasoning can vary with the broth and the amount of moisture in the onions, so dilute it gradually and taste as you go.

How much water should I add to the concentrate?

Start with equal parts concentrate and water or broth by volume: 1 cup (240 ml) of each makes about 2 cups (480 ml) of soup. Use less liquid for a richer bowl or more for a lighter one. If you are using the concentrate in another recipe, add it in small amounts and account for its salt before seasoning the rest of the dish.

Can I make condensed French onion soup without wine?

Yes. Leave out the wine and use 1/2 cup (120 ml) additional broth. To replace some of the acidity, stir in 1 teaspoon (5 ml) cider vinegar or lemon juice near the end of cooking. The substitute keeps the soup balanced, although it will not have the same flavor as wine cooked down with the onions.

Why are my onions not turning brown?

They may be releasing water faster than it can evaporate, especially if the pot is crowded or the heat is very low. Keep the pot uncovered, use a wide cooking surface, and continue cooking until the liquid has cooked off. Stir regularly, but let the onions sit against the hot pot between stirs so they have a chance to brown. Avoid turning the heat up so high that they scorch.

Can I use this in place of canned condensed soup?

You can use it as an onion-forward substitute in many recipes, but it may not match a canned soup’s thickness, salt level, or exact volume. Begin with a smaller amount than the recipe calls for, then add broth or water to reach the needed consistency. If the recipe relies on condensed soup as a thickener, you may need a little extra flour or another thickener, depending on the dish.

Can I make the soup ahead?

Yes. The concentrate can be made a few days ahead and kept refrigerated, or frozen in portions for later use. Its flavor remains useful after chilling, though the onions may soften further and the mixture will thicken. Reheat it gently, dilute it just before serving, and check the seasoning again because added water or broth changes the balance.

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