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Onion Soup

A creamy onion soup made with Spanish onions, butter, water, flour, milk or cream, seasoned with pepper and sea salt.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 7 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 ↓

Onion Soup

Ingredients

Directions

Prepare the onions

  1. Peel and slice the onions from top to bottom.

  2. Fry the onions in butter until soft but not discolored.

Make the soup

  1. Boil the onions in water until quite soft.

  2. Puree the mixture through a fine sieve.

  3. Return the puree to a saucepan.

  4. Bring to a boil.

  5. Stir in the flour to thicken.

  6. Add the milk or cream.

  7. Season with pepper and salt to taste.

  8. Let the soup boil.

Serve

  1. Serve with fried croutons of bread.

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

    Shared aroma: isobutyraldehyde (malty, green).

  5. Onion + buttertop 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

Onions
Form the bulk of the soup, providing its sweetness and body when softened and pureed.
Butter or dripping
Fat that softens the onions gently and carries their flavour.
Flour
Thickens the soup as it heats, giving it a smooth, body-rich texture.
Milk or cream
Adds richness and creaminess, softening the flavour and smoothing the texture.

The step that matters

Fry the onions until soft but not discolored. Browning the onions adds a darker, bitter-tinged flavour and colour; keeping them pale yields a mild, sweet soup.

Swap the onion

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

  1. Potatofits better
  2. Capsicumfits better
  3. Chivefits better
  4. Onionthe original

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