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Onion Soup

A savory soup made from sliced onions, butter, flour, stock, parsley, salt, pepper, eggs, and croutons.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 9 ingredients
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Why it works: Parsley and pepper match in chemistry and in kitchens. They rank in the top 2% of all ingredient pairs, and cooks put them together in 34,122 recipes. Both carry 4'-methylacetophenone, which smells bitter almond. The science ↓

Onion Soup

Ingredients

Directions

Prepare the soup

  1. Slice the onion.

  2. Fry the sliced onion in butter until soft.

  3. Add flour and blend well.

  4. Pour in the stock.

  5. Add parsley.

  6. Season with salt and pepper.

  7. Boil for 15 minutes.

  8. Strain the soup.

Finish and serve

  1. Pour the strained soup over beaten egg yolks.

  2. Serve with croutons.

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. Parsley + peppertop 2% of all pairs
    Smell alikestrong
    Cooked together34,122 recipes

    Shared aroma: 4'-methylacetophenone (bitter almond).

  2. Onion + parsleytop 9% of all pairs
    Smell alikemoderate
    Cooked together25,843 recipes

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

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

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

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

    Shared aroma: isobutyraldehyde (malty, green).

  5. Flour + parsleytop 12% of all pairs
    Smell alikemoderate
    Cooked together16,675 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

Butter
Fat that softens the onion and carries its flavour into the soup.
Flour
Thickens the butter and onion base so the soup becomes body-rich rather than watery.
Stock
Forms the liquid base of the soup and supplies most of its savoury flavour.
Eggs
Egg yolks thicken the finished soup when stirred in as the soup is poured over them.
Spanish onion
Main flavour source; frying softens it and brings out sweetness.

The step that matters

Pouring the soup over the egg yolks. Egg yolks set when heated, so pouring hot soup over them slowly and stirring keeps them from scrambling. Adding them to very hot soup can curdle them.

Swap the onion

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

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

Fit is the average pairing score against butter, flour, parsley, pepper, 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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