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Onion Soup

A simple onion soup made with butter, flour, water, and toasted 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 a skillet over medium heat.

  2. Add butter and chopped onions; stir constantly until onions are browned.

  3. Sprinkle in flour, salt, and pepper; stir until flour is browned.

  4. Pour in cold water while stirring briskly; bring to a boil and cook for 4 minutes.

Serve

  1. Serve immediately over toasted 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 + 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. Onion + buttertop 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, savory flavor that defines the soup.
Butter
Carries the onions as they brown and adds richness to the broth.
Flour
Browned with the onions, it helps thicken the soup as it meets the water.
Toasted bread
Soaks up the broth and gives the soup a firmer, chewier body when served.

The step that matters

Browning the onions. Stirring constantly and keeping the heat moderate lets the onion sugars caramelize evenly. Burnt spots turn bitter, and pale onions give a flat-tasting soup.

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

French 31Brown 15with Milk 7White 5Bavarian 4Bermuda 4 See all 236 →

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