Name: Onion Soup
Ingredients: 4 large onions, chopped; ½ cup butter; 1 quart soup stock; 1 pint boiling milk; 2 tablespoons grated parmesan cheese; ¼ loaf French bread, thinly sliced and dried

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

Fry the onions in butter for 1 hour, stirring often, without browning.
Add seasoning and stock, then cook for another 30 minutes.
Stir in the boiling milk.
Place the dried bread and cheese in a tureen.
Add the beaten egg yolks last, then pour the soup into the tureen and serve.

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.

Butter + breadtop 7% of all pairs

Smell alikemoderate

Cooked together27,232 recipes

Shared aroma: delta-decalactone (sweet, creamy).
Butter + milktop 7% of all pairs

Smell alikemoderate

Cooked together81,283 recipes

Shared aroma: (z)-4-heptenal (biscuit, cream).
Butter + parmesan cheesetop 9% of all pairs

Smell alikemoderate

Cooked together4,163 recipes

Shared aroma: guaiacol (smoky, sweet).
Milk + breadtop 11% of all pairs

Smell alikemoderate

Cooked together11,466 recipes

Shared aroma: 2-undecenal (sweet).
Parmesan cheese + breadtop 15% of all pairs

Smell alikemoderate

Cooked together577 recipes

Shared aroma: guaiacol (smoky, sweet).

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

Swap the onion

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

Tomatofits better
Potatofits better
Asparagusfits better
Onionthe original

Fit is the average pairing score against butter, milk, parmesan cheese, bread. Candidates are from the same food group and used in at least 100 recipes.