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
Make the soup
In a pot, fry the chopped onions in butter without browning them.
Add cold water and parsley, then boil until the onions are soft, about 2 hours.
Strain the mixture and add milk.
Thicken and finish
Thicken with corn starch or flour dissolved in cold water, then cook for 10 minutes.
Just before serving, stir in the remaining butter.
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 + parsleytop 9% of all pairsSmell alikemoderateCooked together25,843 recipes
Shared aroma: 2,4-decadienal (seaweed).
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Milk + corntop 10% of all pairsSmell alikemoderateCooked together6,955 recipes
Shared aroma: hexanal (green, grassy).
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Parsley + corntop 12% of all pairsSmell alikemoderateCooked together943 recipes
Shared aroma: 2,4-decadienal (seaweed).
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Onion + corntop 13% of all pairsSmell alikemoderateCooked together4,205 recipes
Shared aroma: hexanal (green, grassy).
Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs
What each ingredient does
- Onions
- Provide the main flavor and body of the soup as they soften during long simmering.
- Butter
- Adds richness and carries flavor when used to fry the onions and finish the soup.
- Milk
- Adds creaminess and a mild sweetness to the soup base.
- Corn starch or flour
- Thickens the liquid as it cooks, giving the soup a smoother body.
The step that matters
Fry the onions without browning them. Browning would add bitter, caramelized notes that change the soup's mild, delicate flavor. Gentle cooking keeps the onions sweet and pale.
Swap the parsley
How well each one fits the dish's main ingredients (onion, butter, milk, corn):
- Cinnamonfits better
- Garlicfits better
- Thymefits about as well
- Parsleythe original
Fit is the average pairing score against onion, butter, milk, corn. 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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