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French Onion Soup

A soup made from sliced onions, butter, flour, water, salt, pepper, and bread, served over a buttered bread mixture.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 8 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 ↓

French Onion Soup

Ingredients

Directions

Prepare the onions

  1. Peel and thinly slice the onions.

  2. Parboil the onions in boiling water for 10 minutes, then drain.

Make the soup

  1. Melt the butter in a saucepan and cook the onions over high heat until lightly colored.

  2. Stir in the flour and cook for 2 minutes.

  3. Add the water, salt, and pepper; stir until boiling.

  4. Reduce heat and simmer for 5 minutes.

Serve

  1. In a tureen, combine the bread and butter, stirring lightly to melt the butter.

  2. Serve the soup over the bread mixture.

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

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

  3. Butter + flourtop 12% of all pairs
    Smell alikelow
    Cooked together124,287 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 + breadtop 15% of all pairs
    Smell alikemoderate
    Cooked together8,676 recipes

    Shared aroma: 2,4-decadienal (seaweed).

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 body and sweet, caramelized flavor of the soup.
Butter
Adds richness and helps the onions brown lightly in the pan.
Flour
Thickens the cooking liquid so the soup has body.
Bread
Soaks up the soup and gives the dish its substance when served over it.

The step that matters

Cooking the onions until lightly colored. Browning the onions over high heat develops sweet, deep flavors through the Maillard reaction. Pale onions make a flat-tasting soup, while over-darkened ones turn bitter.

Swap the onion

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

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

Fit is the average pairing score against butter, flour, 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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