Why it works: Onion and potato are a kitchen classic. They rank in the top 3% of all ingredient pairs, and 9,023 recipes mention both. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓
Onion Soup
Ingredients
Directions
Make the onion base
Slice two or three large onions.
Fry the sliced onions in a tablespoonful of butter or drippings until they are soft and red.
Add three tablespoonfuls of flour and stir until it is a little cooked.
Add a pint of boiling water slowly, stirring all the time, so it will be smooth.
Add the potato and milk
Boil and mash three good-sized potatoes.
Add a quart of scalded milk slowly to the mashed potatoes, stirring well so it will be smooth.
Add the potato and milk mixture to the onion mixture.
Season with salt and pepper.
Finish and serve
Let the soup get very hot, then pass it through a strainer into the tureen.
Sprinkle over the top a little finely chopped parsley and a few croutons.
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. See the original page.
Explore the science
The flavor team
The pairs that carry this dish. Each one is judged two ways: how much aroma chemistry they share, and how many recipes mention both.
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Onion + potatotop 3% of all pairsAroma overlapmoderateMentioned together9,023 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Butter + milktop 7% of all pairsAroma overlapmoderateMentioned together81,283 recipes
Shared aroma: (z)-4-heptenal (biscuit, cream).
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Potato + peppertop 9% of all pairsAroma overlapmoderateMentioned together8,305 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Milk + potatotop 9% of all pairsAroma overlapmoderateMentioned together3,611 recipes
Shared aroma: (e,z)-2,6-nonadienal (cucumber, melon).
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Onion + peppertop 11% of all pairsAroma overlapmoderateMentioned together68,474 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs
What each ingredient does
- Onions
- Softened in butter, they build the sweet, savory base of the soup.
- Flour
- Cooked with the onions, it thickens the soup and gives it body.
- Potatoes
- Mashed into the liquid, they add starch that gives a thick, smooth texture.
- Milk
- Adds richness and creaminess, softening the soup's flavor and mouthfeel.
- Butter
- Fat for frying the onions, carrying flavor and helping them brown and soften.
The step that matters
Adding the water and milk slowly while stirring. Adding liquid to a flour-thickened base all at once can form lumps, because flour clumps when it meets liquid. Slow addition with constant stirring disperses the starch evenly so the soup stays smooth.
“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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