Why it works: Onion and potato are a kitchen classic. They rank in the top 3% of all ingredient pairs, and cooks put them together in 9,023 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓
Onion Soup
Ingredients
Directions
Melt the butter in a skillet and fry the sliced onions until brown.
Stir in the flour and mix well.
Transfer the mixture to a large pot and slowly stir in the boiling milk (or water).
Place the pot in a kettle of boiling water.
Season with salt and pepper, then add the grated potato.
Cook for 5 to 10 minutes.
Stir in the sweet cream and serve immediately.
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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Onion + potatotop 3% of all pairsSmell alikemoderateCooked together9,023 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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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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Butter + creamtop 8% of all pairsSmell alikemoderateCooked together41,516 recipes
Shared aroma: delta-dodecalactone (sweet, creamy).
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Pepper + potatotop 9% of all pairsSmell alikemoderateCooked together8,305 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Milk + potatotop 9% of all pairsSmell alikemoderateCooked together3,611 recipes
Shared aroma: (e,z)-2,6-nonadienal (cucumber, melon).
Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs
What each ingredient does
- Onions
- Browned onions provide the soup's main sweet, savoury flavour.
- Butter
- Fat that carries flavour and helps the onions brown in the skillet.
- Flour
- Thickens the milk mixture into a smooth, body-rich soup.
- Milk
- Forms the liquid base of the soup and adds creamy richness.
- Grated potato
- Releases starch that adds further body and thickness to the soup.
- Sweet cream
- Stirred in at the end to add richness and a smooth, silky texture.
The step that matters
Browning the onions. Onions must be cooked until deeply browned because the browning reactions develop the sweet, savoury flavour the soup depends on. Pale onions make a flat-tasting soup.
Swap the onion
How well each one fits the dish's main ingredients (butter, flour, milk, pepper, potato, cream):
- Chivefits about as well
- Leekfits about as well
- Spinachfits about as well
- Onionthe original
Fit is the average pairing score against butter, flour, milk, pepper, potato, cream. 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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