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
Prepare the onions
Peel and finely mince the onions.
Make the soup
In a pot, melt the butter and sauté the onions until tender but not browned.
Add the seasoned stock, cayenne, salt, and pepper; simmer for 20 minutes.
Strain the soup through a fine sieve back into the pot.
Grate the stale bread into the boiling milk or cream, then stir it into the soup.
Serve hot.
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.
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Butter + milktop 7% of all pairsSmell alikemoderateCooked together81,283 recipes
Shared aroma: (z)-4-heptenal (biscuit, cream).
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Onion + peppertop 11% of all pairsSmell alikemoderateCooked together68,474 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Onion + buttertop 15% of all pairsSmell alikemoderateCooked together42,912 recipes
Shared aroma: decanal (soap, orange peel).
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Onion + milktop 20% of all pairsSmell alikemoderateCooked together13,418 recipes
Shared aroma: hexanal (green, grassy).
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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
- Spanish onions
- Provide the main body and sweet, savoury flavour of the soup as they soften.
- Stale bread crumb
- Thickens the soup as it absorbs liquid, giving it body.
- Milk or cream
- Adds richness and a smooth, mellow texture to the finished soup.
- Butter
- Adds fat and flavour while the onions soften gently in the pot.
The step that matters
Sauté the onions until tender but not browned. Cooking onions slowly in butter draws out their sweetness. Browning them would add bitter, toasted notes that change the soup's clean, mild flavour.
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.
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