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Soubise Soup

A creamy onion soup made with sautéed onions, butter, flour, milk, and seasonings.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 8 ingredients
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Why it works: Butter and milk are a kitchen classic. They rank in the top 7% of all ingredient pairs, and cooks put them together in 81,283 recipes. Both carry (z)-4-heptenal, which smells biscuit, cream. The science ↓

Soubise Soup

Ingredients

Directions

Cook the onions

  1. Combine sliced onions, 1 tablespoon butter, and water in a saucepan.

  2. Simmer gently until onions are soft enough to pass through a sieve.

Make the sauce

  1. Melt 2 tablespoons butter in a fresh saucepan.

  2. Stir in 2 tablespoons flour, 1 teaspoon coarse sea salt, and ½ teaspoon white pepper until bubbling.

  3. Gradually add 2 cups milk, stirring until mixture thick and smooth.

Combine and serve

  1. Add the pulped onion to the mixture.

  2. Taste for seasoning.

  3. Keep hot over boiling water.

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 + milktop 7% of all pairs
    Smell alikemoderate
    Cooked together81,283 recipes

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

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

    Shared aroma: isobutyraldehyde (malty, green).

  3. Flour + milktop 14% of all pairs
    Smell alikelow
    Cooked together78,219 recipes

    Shared aroma: isobutyraldehyde (malty, green).

  4. Onion + buttertop 15% of all pairs
    Smell alikemoderate
    Cooked together42,912 recipes

    Shared aroma: decanal (soap, orange peel).

  5. Onion + flourtop 17% of all pairs
    Smell alikemoderate
    Cooked together32,460 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

White onions
Provide the main body and sweet, mellow flavour once softened and pulped.
Butter
Adds richness and carries flavour in both the onion base and the roux.
All-purpose flour
Thickens the milk into a smooth sauce when cooked with the butter.
Milk
Forms the creamy liquid that the flour thickens into the soup's base.

The step that matters

Stirring the milk into the roux. Adding cold milk gradually while stirring keeps the flour evenly dispersed, so the sauce becomes smooth rather than lumpy as the starch swells and thickens.

Swap the white pepper

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

  1. Cinnamonfits better
  2. Capersfits better
  3. Garlicfits better
  4. White pepperthe original

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