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Onion Soup

A creamy onion soup with butter, stock, milk, egg yolks, and toasted bread topped with Parmesan.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 9 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

Cook the onions

  1. In a large pot, slowly stir the onions in the butter over low heat for one hour, stirring frequently to avoid burning.

  2. Add salt, cayenne, and soup stock, then cook for an additional hour.

  3. Add one-third as much stock as you used before.

Assemble and serve

  1. In a tureen, place the dried bread and grated cheese.

  2. Beat the egg yolks with a ladleful of the soup, then pour this mixture over the bread.

  3. Cover and let it sit for five minutes.

  4. Add the remaining soup 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. Butter + milktop 7% of all pairs
    Smell alikemoderate
    Cooked together81,283 recipes

    Shared aroma: (z)-4-heptenal (biscuit, cream).

  3. Butter + parmesan cheesetop 9% of all pairs
    Smell alikemoderate
    Cooked together4,163 recipes

    Shared aroma: guaiacol (smoky, sweet).

  4. Milk + breadtop 11% of all pairs
    Smell alikemoderate
    Cooked together11,466 recipes

    Shared aroma: 2-undecenal (sweet).

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

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

Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs

What each ingredient does

Onions
Their sugars caramelize slowly, giving the soup its sweet, deep, browned flavor.
Butter
Cooks the onions gently and adds richness to the soup.
Egg yolks
Enrich and thicken the soup as they set gently in the hot liquid.
French bread
Soaks up the broth, giving the soup body and a bready texture.
Parmesan cheese
Adds savory, salty depth and melts into the bread.
Soup stock
Forms the liquid base that the onions simmer in.

The step that matters

Cooking the onions slowly. Low heat and frequent stirring let the onions' sugars caramelize gradually into sweet, brown flavor. Higher heat or neglect scorches the sugars, leaving a bitter taste.

Swap the onion

How well each one fits the dish's main ingredients (butter, pepper, milk, egg, bread, parmesan cheese):

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

Fit is the average pairing score against butter, pepper, milk, egg, bread, parmesan cheese. 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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