Name: Brown Fish Sauce
Ingredients: 1 large onion, peeled and sliced; 2 tablespoons butter; 1 teaspoon flour; ½ cup water; ¼ teaspoon coarse sea salt; ¼ teaspoon black pepper; ½ teaspoon mushroom ketchup

Why it works: Butter and mushroom are a kitchen classic. They rank in the top 7% of all ingredient pairs, and cooks put them together in 12,525 recipes. Both carry trans-2-decenal, which smells waxy, orange. The science ↓

Brown Fish Sauce

Ingredients

Directions

In a skillet, melt the butter over medium heat.
Add the sliced onion and fry until browned but not crisp.
Sprinkle the flour over the onions and stir.
Slowly add the water while stirring to avoid lumps.
Season with salt and black pepper, and cook for a few minutes.
Stir in the mushroom ketchup and mix well.

Recipe from a historical cookbook (Internet Archive).

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.

Butter + mushroomtop 7% of all pairs

Smell alikemoderate

Cooked together12,525 recipes

Shared aroma: trans-2-decenal (waxy, orange).
Onion + mushroomtop 10% of all pairs

Smell alikemoderate

Cooked together10,626 recipes

Shared aroma: 2,4-decadienal (seaweed).
Onion + peppertop 11% of all pairs

Smell alikemoderate

Cooked together68,474 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Pepper + mushroomtop 11% of all pairs

Smell alikemoderate

Cooked together13,580 recipes

Shared aroma: 2-nonenal (fatty, green).
Butter + flourtop 12% of all pairs

Smell alikelow

Cooked together124,287 recipes

Shared aroma: isobutyraldehyde (malty, green).

Butter and flour 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

Swap the onion

How well each one fits the dish's main ingredients (butter, flour, pepper, mushroom, ketchup):

Shallotfits better
Capsicumfits better
Chivefits better
Onionthe original

Fit is the average pairing score against butter, flour, pepper, mushroom, ketchup. Candidates are from the same food group and used in at least 100 recipes.