Name: Sardine Sandwiches
Ingredients: 3 hard boiled eggs; 1 can sardines; a speck of cayenne pepper; a pinch of salt; ¼ teaspoon dry mustard; lemon juice (enough to make a paste); thin slices of bread; butter; lettuce leaves (optional)

Why it works: Mustard and lettuce match in chemistry and in kitchens. They rank in the top 1% of all ingredient pairs, and cooks put them together in 1,356 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓

Sardine Sandwiches

Ingredients

Directions

Prepare the filling

Mince the hard boiled eggs and sardines together.
Add cayenne pepper, salt, dry mustard, and lemon juice to form a paste.

Assemble

Butter the thin slices of bread.
Spread the sardine mixture between the slices.
Add a lettuce leaf for an improvement, if desired.

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.

Mustard + lettucetop 1% of all pairs

Smell alikestrong

Cooked together1,356 recipes

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

Smell alikestrong

Cooked together27,047 recipes

Shared aroma: trans-2-nonenal (cardboard, fatty).
Bread + buttertop 7% of all pairs

Smell alikemoderate

Cooked together27,232 recipes

Shared aroma: delta-decalactone (sweet, creamy).
Pepper + mustardtop 9% of all pairs

Smell alikemoderate

Cooked together15,430 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Pepper + lettucetop 9% of all pairs

Smell alikemoderate

Cooked together4,037 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

Hard boiled eggs: Provide body and bulk, giving the filling a firm, spreadable texture.
Sardines: Supply the main savoury, oily flavour and richness to the filling.
Lemon juice: Adds acidity that brightens the fish and helps bind the mixture into a paste.
Butter: Adds fat and moisture to the bread, keeping it from soaking up the filling.

Swap the lettuce

The recipe marks lettuce as optional. How well each one fits the dish's main ingredients (egg, pepper, mustard, lemon, bread, butter):

Shallotfits better
Asparagusfits better
Spinachfits about as well
Lettucethe original

Fit is the average pairing score against egg, pepper, mustard, lemon, bread, butter. 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.