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Onion Soup

A soup made with sliced onions, butter, flour, milk, water, and seasoned with salt and pepper, served over bread slices.

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 pan over medium heat.

  2. Add the sliced onions and fry until light yellow but not brown.

  3. Stir in the flour and cook until it turns light brown, stirring constantly.

  4. Gradually pour in the milk and water, then season with salt and pepper.

  5. Allow the mixture to boil for at least 15 minutes.

Serve

  1. Serve the boiling soup over thin slices of bread.

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. Butter + milktop 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. Onion + peppertop 11% of all pairs
    Smell alikemoderate
    Cooked together68,474 recipes

    Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).

  5. Butter + flourtop 12% of all pairs
    Smell alikelow
    Cooked together124,287 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 sweetness and savory flavor as they soften and lightly color in the butter.
Butter
Carries the onions and adds richness and aroma from its fat.
Flour
Browned with the fat, it thickens the milk and water into a smooth, body-rich soup.
Milk
Adds creaminess and body to the broth, softening its flavor.
Bread
Soaks up the hot soup, giving the dish substance and a soft texture.

The step that matters

Browning the flour. Stirring constantly keeps the flour from scorching and lumping. Cooking it in the fat until light brown removes raw starch taste and helps it thicken the liquid smoothly once the milk and water are added.

Swap the onion

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

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

Fit is the average pairing score against butter, flour, milk, pepper, 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.

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