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 Sauce
Ingredients
Directions
Prepare the onions
Skin the onions and boil them in plenty of water until soft.
Remove the onions from the water and chop them very finely.
Make the sauce
In a saucepan, melt the butter, then stir in the flour to make a roux.
Gradually add the milk or broth, stirring until smooth.
Stir in the chopped onions and season with pepper and coarse sea salt.
Serve as needed.
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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Flour + buttertop 12% of all pairsSmell alikelowCooked together124,287 recipes
Shared aroma: isobutyraldehyde (malty, green).
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Flour + milktop 14% of all pairsSmell alikelowCooked together78,219 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).
Flour and butter 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 flavour and soft, pulpy body of the sauce.
- Flour
- Thickens the butter and milk or broth into a smooth, stable sauce.
- Butter
- Forms the fat base for the roux and adds richness to the sauce.
- Milk or broth
- Makes up the liquid of the sauce, setting its volume and creaminess.
The step that matters
Gradually add the milk or broth, stirring until smooth. Adding liquid all at once to a roux can trap flour in lumps. Adding it slowly while stirring lets the starch disperse evenly, giving a smooth, thickened sauce.
Swap the onion
How well each one fits the dish's main ingredients (flour, butter, milk, pepper):
- Potatofits better
- Capsicumfits better
- Chivefits better
- Onionthe original
Fit is the average pairing score against flour, butter, milk, pepper. 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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