Name: Egg Sandwich Filling
Ingredients: 4 hard-boiled egg yolks; 3 tablespoons finely chopped celery; ½ tablespoon melted butter or olive oil; 1 tablespoon minced parsley; ½ teaspoon onion juice; ¾ teaspoon salt; ⅛ teaspoon white pepper

Why it works: Celery and parsley match in chemistry and in kitchens. They rank in the top 1% of all ingredient pairs, and cooks put them together in 6,810 recipes. Both carry 4'-methylacetophenone, which smells bitter almond. The science ↓

Egg Sandwich Filling

Ingredients

4 hard-boiled egg yolks
3 tablespoons finely chopped celery
½ tablespoon melted butter or olive oil
1 tablespoon minced parsley
½ teaspoon onion juice
¾ teaspoon salt
⅛ teaspoon white pepper

Directions

Cook the yolks

Separate the yolks from the whites of the eggs carefully.
Place each yolk in half of its shell and gently drop into simmering water.
Cook the yolks slowly for 20 minutes.
If a shell tilts, leave it undisturbed.

Make the filling

Remove the hard-cooked yolks from the shells and rub through a sieve.
Mix all ingredients together for the filling.

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.

Celery + parsleytop 1% of all pairs

Smell alikestrong

Cooked together6,810 recipes

Shared aroma: 4'-methylacetophenone (bitter almond).
Celery + oniontop 7% of all pairs

Smell alikemoderate

Cooked together18,518 recipes

Shared aroma: guaiacol (smoky, sweet).
Parsley + oniontop 9% of all pairs

Smell alikemoderate

Cooked together25,843 recipes

Shared aroma: 2,4-decadienal (seaweed).
Parsley + white peppertop 14% of all pairs

Smell alikelow

Cooked together1,451 recipes

Shared aroma: myrcene (balsamic, herbaceous).
Butter + oniontop 15% of all pairs

Smell alikemoderate

Cooked together42,912 recipes

Shared aroma: decanal (soap, orange peel).

Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs

What each ingredient does

Egg yolks: Provide the main body and rich, creamy texture of the filling as they set when cooked.
Celery: Adds a crisp, fresh crunch that contrasts with the soft, smooth yolk mixture.
Butter or olive oil: Adds fat for moisture, richness and a smoother mouthfeel in the filling.
Onion juice: Adds a sharp aromatic flavour that brightens the rich yolks.

The step that matters

Cook the yolks slowly in simmering water. Gentle heat sets the yolks evenly and keeps them tender. Boiling hard or overcooking can make yolks dry and crumbly and cause a grey-green ring, which makes them harder to rub smooth through a sieve.

Swap the white pepper

How well each one fits the dish's main ingredients (egg, celery, butter, parsley, onion):

Thymefits better
Tarragonfits better
Capersfits better
White pepperthe original

Fit is the average pairing score against egg, celery, butter, parsley, onion. 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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Egg Sandwich Filling