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Onion Soup

A savory soup made with onions, stock, milk, butter, flour, and croutons.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 7 ingredients
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Why it works: Butter and bread are a kitchen classic. They rank in the top 7% of all ingredient pairs, and cooks put them together in 27,232 recipes. Both carry delta-decalactone, which smells sweet, creamy. The science ↓

Onion Soup

Ingredients

Directions

Make the soup

  1. Melt the butter in a saucepan.

  2. Add the sliced onions and sauté until tender.

  3. Sprinkle in the flour, stirring to create a roux.

  4. Add the stock and stir over high heat until boiling.

  5. Simmer until the onions are tender.

  6. Pass the mixture through a sieve back into the saucepan.

  7. Reheat, add the milk, and season to taste.

Serve

  1. Serve with croutons.

Recipe from a historical cookbook (Internet Archive).

Transcribed from a scanned cookbook and modernised for today's kitchens. Where the book gave no heat or time, or said "a moderate oven", the temperatures and times here may be modern equivalents rather than the book's own figures.

Explore the science

The flavor team

The pairs that carry this dish. Each one is judged two ways: how much their aromas overlap, and how often cooks already put them together.

  1. Butter + breadtop 7% of all pairs
    Smell alikemoderate
    Cooked together27,232 recipes

    Shared aroma: delta-decalactone (sweet, creamy).

  2. Milk + buttertop 7% of all pairs
    Smell alikemoderate
    Cooked together81,283 recipes

    Shared aroma: (z)-4-heptenal (biscuit, cream).

  3. Milk + breadtop 11% of all pairs
    Smell alikemoderate
    Cooked together11,466 recipes

    Shared aroma: 2-undecenal (sweet).

  4. Butter + flourtop 12% of all pairs
    Smell alikelow
    Cooked together124,287 recipes

    Shared aroma: isobutyraldehyde (malty, green).

  5. Milk + flourtop 14% of all pairs
    Smell alikelow
    Cooked together78,219 recipes

    Shared aroma: isobutyraldehyde (malty, green).

Butter and flour barely smell alike, yet cooks put them together in 124,287 recipes: they work on texture and structure more than aroma.

Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs

What each ingredient does

Onions
Provide the main flavour and body of the soup as they soften and sweeten.
Flour
Forms a roux with the butter that thickens the stock.
Stock
Forms the liquid base of the soup.
Milk
Adds richness and smooths the texture when added at the end.
Butter
Carries the onion flavour and forms the base of the roux.

The step that matters

Sprinkle in the flour, stirring to create a roux. Flour added to hot butter must be stirred constantly so it coats the fat evenly; otherwise it clumps and the soup thickens unevenly.

Swap the onion

How well each one fits the dish's main ingredients (milk, butter, flour, bread):

  1. Potatofits better
  2. Leekfits better
  3. Shallotfits better
  4. Onionthe original

Fit is the average pairing score against milk, butter, flour, bread. Candidates are from the same food group and used in at least 100 recipes.

“What each ingredient does” and “The step that matters” were written by Claude from this recipe’s own method and reviewed in samples by CompKitchen.

More onion soup recipes

French 31Brown 15with Milk 7White 5Bavarian 4Bermuda 4 See all 236 →

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