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Onion Soup

A soup made with sliced onions, butter, flour, veal stock, salt, and an egg.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 6 ingredients
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Why it works: Butter and flour are a kitchen classic. They rank in the top 12% of all ingredient pairs, and cooks put them together in 124,287 recipes. Both carry isobutyraldehyde, which smells malty, green. The science ↓

Onion Soup

Ingredients

Directions

Prepare

  1. Slice the onions very thinly.

  2. In a large pot, melt the butter over medium heat.

  3. Add the sliced onions and flour.

  4. Cook until tender.

Make the soup

  1. Pour in the veal stock and bring to a boil for 20 minutes.

  2. Skim off any foam.

  3. Season with salt.

  4. Whisk in the beaten egg to thicken the soup.

  5. Reduce heat.

  6. Let it simmer before serving.

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

    Shared aroma: isobutyraldehyde (malty, green).

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

    Shared aroma: decanal (soap, orange peel).

  3. Flour + eggtop 15% of all pairs
    Smell alikelow
    Cooked together106,462 recipes

    Shared aroma: isobutyraldehyde (malty, green).

  4. Butter + eggtop 17% of all pairs
    Smell alikemoderate
    Cooked together118,967 recipes

    Shared aroma: decanal (soap, orange peel).

  5. Onion + vealtop 17% of all pairs
    Smell alikelow
    Cooked together6,841 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 sweetness as they soften and caramelize slowly.
Butter
Adds fat and richness and helps the onions cook gently without sticking.
Flour
Coats the onions and thickens the soup as it cooks into the stock.
Veal stock
Forms the liquid base of the soup and carries its savory flavor.
Egg
Thickens the soup slightly and adds richness when whisked in.

The step that matters

Whisk in the beaten egg. Egg proteins set when heated, so adding it to boiling soup can curdle it. Lower the heat first and whisk steadily so the egg thickens smoothly.

Swap the onion

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

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

Fit is the average pairing score against butter, flour, veal, egg. 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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