Why it works: Butter and cheese are a kitchen classic. They rank in the top 8% of all ingredient pairs, and cooks put them together in 7,962 recipes. Both carry delta-dodecalactone, which smells sweet, creamy. The science ↓
Onion Soup
Ingredients
Directions
Make the soup
Peel and cut the onions into small pieces.
In a stewpan, melt the butter and fry the onions until golden.
Mix the flour with water and add to the pan.
Fill with water to make 3 pints and let it boil gently until the onions are soft and the soup thickens.
Season with salt and pepper.
Assemble and serve
Line the bottom of a soup tureen with sliced French roll or stale crusts.
Pour the soup over the bread and cover with grated cheese.
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 + cheesetop 8% of all pairsSmell alikemoderateCooked together7,962 recipes
Shared aroma: delta-dodecalactone (sweet, creamy).
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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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Butter + flourtop 12% of all pairsSmell alikelowCooked together124,287 recipes
Shared aroma: isobutyraldehyde (malty, green).
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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 + cheesetop 16% of all pairsSmell alikemoderateCooked together4,849 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Butter and flour barely smell alike, yet cooks put them together in 124,287 recipes: they work on texture and structure more than aroma.
Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs
What each ingredient does
- Onions
- Provide the main body and sweetness of the soup as they soften and caramelise when fried.
- Butter
- Fats the onions so they fry to a golden colour and add richness to the soup.
- Flour
- Thickens the water-based broth into a soup as it cooks.
- French roll or stale crusts
- Soaks up the soup and forms a bread base in the tureen.
- Grated cheese
- Melts over the top and browns, adding fat and savoury flavour.
The step that matters
Fry the onions until golden. Slow frying lets the onions release sugars that brown slowly, building the sweet, deep flavour of the soup. Rushing on high heat can scorch them, leaving a bitter taste, so they need patient, moderate heat.
Swap the onion
How well each one fits the dish's main ingredients (butter, flour, pepper, cheese):
- Capsicumfits better
- Mustardfits better
- Potatofits better
- Onionthe original
Fit is the average pairing score against butter, flour, pepper, 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.
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