Name: Lemon or Orange Filling
Ingredients: 1 lemon (juice and grated rind); 1 cup sugar; 2 egg yolks, beaten; 2 tablespoons milk; a pinch of salt; 1 orange (for orange filling, use juice and grated rind)

Why it works: Lemon and orange match in chemistry and in kitchens. They rank in the top 1% of all ingredient pairs, and cooks put them together in 10,634 recipes. Both carry 3-hexenal, which smells apple, fruity. The science ↓

Lemon or Orange Filling

Ingredients

Directions

Make the filling

In a bowl, mix the lemon juice, grated rind, sugar, beaten egg yolks, milk, and salt.
Cook the mixture in a double boiler, stirring constantly until it thickens.
Let it cool before spreading.

Orange variation

For orange filling, substitute the lemon with the juice and grated rind of one orange and add 2 teaspoons of lemon juice, then follow the same steps.

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.

Lemon + orangetop 1% of all pairs

Smell alikestrong

Cooked together10,634 recipes

Shared aroma: 3-hexenal (apple, fruity).
Lemon + milktop 15% of all pairs

Smell alikemoderate

Cooked together19,053 recipes

Shared aroma: 2-nonenal (fatty, green).
Milk + orangetop 15% of all pairs

Smell alikemoderate

Cooked together4,696 recipes

Shared aroma: 1-octen-3-one (mushroom, metallic).
Lemon + sugartop 18% of all pairs

Smell alikelow

Cooked together53,532 recipes

Shared aroma: 2-nonenal (fatty, green).
Egg + milktop 18% of all pairs

Smell alikemoderate

Cooked together88,785 recipes

Shared aroma: 2-nonenal (fatty, green).

Lemon and sugar barely smell alike, yet cooks put them together in 53,532 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

What each ingredient does

Egg yolks: Thicken the custard as they set during gentle cooking and add richness.
Sugar: Sweetens the filling and balances the sharpness of the citrus.
Lemon: Provides the bright acidity and aroma that define the filling.

The step that matters

Cook in a double boiler, stirring constantly until it thickens. Egg yolks can curdle or scramble if overheated. Gentle indirect heat and constant stirring let the yolks thicken the mixture smoothly.

Swap the orange

How well each one fits the dish's main ingredients (lemon, sugar, egg, milk):

Vanillafits better
Orangethe original
Figfits about as well
Blueberryfits about as well

Fit is the average pairing score against lemon, sugar, egg, milk. 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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Lemon or Orange Filling