Why it works: Onion and pepper are a kitchen classic. They rank in the top 11% of all ingredient pairs, and cooks put them together in 68,474 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓
Brown Onion Soup
Ingredients
Directions
Prepare the onions
Peel and slice the onions into thin rings.
Fry the onions in butter until tender and brown.
Drain the onions on a sieve to remove excess butter.
Make the soup
In a kettle, combine the onions with 5 quarts of water and boil for 1 hour, stirring often.
Season with salt and pepper to taste.
Rub the crumbs through a colander and add to the soup, stirring continuously to keep it smooth.
Boil for an additional 2 hours.
Finish and serve
Before serving, beat the egg yolks with the vinegar and a little of the soup.
Gradually pour the egg mixture into the soup while stirring continuously.
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 + peppertop 11% of all pairsSmell alikemoderateCooked together68,474 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Onion + vinegartop 14% of all pairsSmell alikemoderateCooked together18,226 recipes
Shared aroma: acetic acid (sour, vinegar).
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Pepper + vinegartop 14% of all pairsSmell alikemoderateCooked together27,814 recipes
Shared aroma: 4'-methylacetophenone (bitter almond).
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Onion + buttertop 15% of all pairsSmell alikemoderateCooked together42,912 recipes
Shared aroma: decanal (soap, orange peel).
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Pepper + teatop 15% of all pairsSmell alikemoderateCooked together260 recipes
Shared aroma: trans-2-nonenal (cardboard, fatty).
Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs
What each ingredient does
- Spanish onions
- Form the bulk of the soup and, once browned and simmered, give it its deep, sweet flavour.
- Butter
- Fat used to fry the onions, helping them brown and develop rich flavour.
- Crumbs of roll or biscuit
- Starch that thickens the soup and gives it body as it cooks.
- Egg yolks
- Enrich and thicken the soup when gently stirred in, adding richness and smoothness.
- Vinegar
- Adds a slight acidity that brightens the rich, sweet onion flavour.
The step that matters
Adding the egg yolk mixture. If the egg is poured in too quickly or the soup is too hot, the yolks can scramble into lumps instead of thickening it smoothly. Tempering with a little hot soup first and stirring constantly keeps the egg yolks evenly dispersed and creamy.
Swap the onion
How well each one fits the dish's main ingredients (butter, pepper, tea, egg, vinegar):
- Capsicumfits better
- Potatofits better
- Mustardfits better
- Onionthe original
Fit is the average pairing score against butter, pepper, tea, egg, vinegar. 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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