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 ↓
Onion Soup
Ingredients
Directions
Make the soup
Brown two onions in a saucepan with one tablespoonful butter.
Stir in a little flour.
Moisten with one and one-half pints white broth.
Season with salt and pepper to taste.
Cook for ten minutes.
Assemble and bake
Place small square of toasted bread in a bowl.
Cover them with fine slices of Swiss cheese.
Pour hot broth over them.
Add a few more slices of cheese on top.
Put in the oven for five minutes before serving.
Nutrition, whole recipe (rough)
What these numbers assume: 4 portions
| Ingredient | Portion assumed | kcal |
|---|---|---|
| Butter | 1 tbsp (14g) | 102 |
| Onion | 1 medium (110g) | 44 |
| Black Pepper | 1 tsp ground (2.3g) | 6 |
| Salt | 1 tsp (6g) | 0 |
One typical portion per ingredient; the recipe's quantities are not counted. A rough guide only, not for medical or dietary planning.
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 their aromas overlap, and how often cooks already put them together.
-
Onion + peppertop 11% of all pairsSmell alikemoderateCooked together68,474 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
-
Butter + oniontop 15% of all pairsSmell alikemoderateCooked together42,912 recipes
Shared aroma: decanal (soap, orange peel).
-
Butter + peppertop 21% of all pairsSmell alikemoderateCooked together85,593 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
- Butter
- Adds fat and helps the onions brown, giving the soup a richer flavor.
- Onions
- Browning them builds sweetness and a deep savory base for the soup.
- Flour (in the method)
- Thickens the broth slightly so it clings to the bread and cheese.
- Swiss cheese (in the method)
- Melts into a stretchy, browned layer that binds the topping together.
- Toasted bread (in the method)
- Soaks up the hot broth and gives the dish a soft, substantial base.
The step that matters
Brown two onions in a saucepan with one tablespoonful butter.. Slow browning lets the onions' natural sugars caramelize and react through the Maillard reaction, creating sweet, deep flavor. Rushing over high heat can scorch them, leaving bitter notes, while stopping too early leaves the soup tasting flat.
Swap the onion
How well each one fits the dish's main ingredients (butter, pepper):
- Capsicumfits better
- Potatofits better
- Carrotfits about as well
- Onionthe original
Fit is the average pairing score against butter, 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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