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
Melt the butter in a stewpan.
Add the sliced onions and fry until nicely browned.
Stir in the rolled crackers and pepper.
Pour in the boiling milk and water.
Let it simmer for 15 minutes and serve.
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 + milktop 7% of all pairsSmell alikemoderateCooked together81,283 recipes
Shared aroma: (z)-4-heptenal (biscuit, cream).
-
Onion + peppertop 11% of all pairsSmell alikemoderateCooked together68,474 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
-
Butter + oniontop 15% of all pairsSmell alikemoderateCooked together42,912 recipes
Shared aroma: decanal (soap, orange peel).
-
Onion + milktop 20% of all pairsSmell alikemoderateCooked together13,418 recipes
Shared aroma: hexanal (green, grassy).
-
Butter + peppertop 21% of all pairsSmell alikemoderateCooked together85,593 recipes
Shared aroma: trans-2-nonenal (cardboard, fatty).
Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs
What each ingredient does
- Butter
- Adds fat and richness, and helps the onions brown in the pan.
- White onions
- Provide the main flavour and sweetness once fried until browned.
- Crackers
- Thicken the soup as they soften in the hot liquid.
- Milk and water
- Form the liquid base that becomes the soup.
The step that matters
Frying the onions until nicely browned. Browning the onions through caramelisation develops deep, sweet flavour. Pale onions give a flat taste, so they need enough time in the fat.
Swap the onion
How well each one fits the dish's main ingredients (butter, pepper, milk):
- Potatofits better
- Capsicumfits better
- Tomatofits about as well
- Onionthe original
Fit is the average pairing score against butter, pepper, milk. 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
You might also like
Tomato Soup526 recipes
Brown Bread461 recipes
Mutton Broth292 recipes
Yorkshire Pudding264 recipesThe free Flavor Lab newsletter: one surprising pairing a week and the molecular reason it works, in 60 seconds. No spam, unsubscribe anytime.
Prefer an account? Create a free account to save pairings and unlock the full chemistry.