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Onion Soup

A simple soup made with butter, onion, stock, flour, salt, pepper, and stale bread.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 7 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. Heat the butter in a frying pan.

  2. Add the chopped onion and fry until browned, being careful not to burn.

  3. In a stew pan, combine the soup stock and fried onion; cook for 15 minutes.

  4. Strain the mixture and return to the heat.

  5. Mix the flour with a little cold water, add to the soup, and boil for 5 minutes.

  6. Season with salt and pepper.

Finish and serve

  1. Cut the stale bread into dice and brown in the oven.

  2. Place the bread in a soup tureen, pour the soup over it, and serve immediately.

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. Butter + oniontop 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

Onion
Browning in butter builds the deep, sweet flavour that defines the soup.
Flour
Mixed with cold water and boiled, it thickens the stock into a smooth body.
Soup stock
Forms the liquid base that carries the flavour and makes up most of the soup.
Stale bread
Dried cubes soak up some broth and add a soft, chewy texture when served.

The step that matters

Browning the onion. Onion should be fried until browned but not burnt. Browning caramelises its sugars for rich flavour, while burnt pieces turn bitter and can spoil the whole pot.

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.

More onion soup recipes

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