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Onion Soup

A savory soup made with onions, butter, flour, water, bread crust, egg yolks, and vinegar.

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 ↓

Onion Soup

Ingredients

Directions

Make the soup

  1. Melt the butter in a stewpan over medium heat until it stops bubbling.

  2. Add the chopped onions and fry for 15 minutes.

  3. Sprinkle in the flour and stir well, cooking for a few more minutes.

  4. Pour in the boiling water and add the bread crust; season with salt.

  5. Boil for 10 minutes, stirring often.

Finish with egg

  1. Remove from heat and beat the egg yolks with the vinegar.

  2. Mix some soup into the egg yolks, then stir this mixture back into the soup.

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

    Shared aroma: isobutyraldehyde (malty, green).

  3. Bread + eggtop 13% of all pairs
    Smell alikemoderate
    Cooked together22,662 recipes

    Shared aroma: (e)-2-octenal (fatty, green).

  4. Onion + vinegartop 14% of all pairs
    Smell alikemoderate
    Cooked together18,226 recipes

    Shared aroma: acetic acid (sour, vinegar).

  5. Butter + oniontop 15% of all pairs
    Smell alikemoderate
    Cooked together42,912 recipes

    Shared aroma: decanal (soap, orange peel).

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

Butter
Fat that carries the onions' flavour and helps them brown gently in the pan.
Onions
Main flavour base; slow frying softens them and builds sweetness and savoury depth.
Flour
Thickens the soup slightly as it cooks with the butter and onions.
Egg yolks
Enrich and thicken the finished soup when tempered in and gently heated.
Bread crust
Adds body to the broth as it softens in the boiling liquid.

The step that matters

Adding the egg yolks. Egg yolks can curdle if added directly to hot liquid. Mixing some soup into them first gradually raises their temperature, so they blend in smoothly and thicken the soup without turning grainy.

Swap the onion

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

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

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

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