Name: Lemon Custard Pie
Ingredients: 1 lemon; 1 cup sugar; 2 eggs, separated; 3 tablespoons flour; milk (enough to make a paste); 4 tablespoons sugar (for meringue); a pinch of baking powder

Why it works: Flour and milk are a kitchen classic. They rank in the top 14% of all ingredient pairs, and cooks put them together in 78,219 recipes. Both carry isobutyraldehyde, which smells malty, green. The science ↓

Lemon Custard Pie

Ingredients

Directions

The book gives no oven temperature. The 350°F (175°C) in the steps was added when the recipe was transcribed, as a starting point.

Prepare the filling

Grate the yellow rind of the lemon, avoiding the bitter white skin.
Squeeze the juice into the sugar and mix well.
Beat the egg yolks and stir them into the lemon-sugar mixture.
Make a paste with the flour and enough milk to fill the pie plate.
Line a pie plate with pie crust and fill it with the lemon mixture.

Bake and top with meringue

Bake in a 350°F (175°C) oven until set.
Beat the egg whites with 4 tablespoons of sugar and a pinch of baking powder until stiff.
Spread the meringue over the custard and return to the oven to brown slightly.

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.

Flour + milktop 14% of all pairs

Smell alikelow

Cooked together78,219 recipes

Shared aroma: isobutyraldehyde (malty, green).
Sugar + flourtop 15% of all pairs

Smell alikemoderate

Cooked together92,116 recipes

Shared aroma: phenylacetaldehyde (hawthorne, honey).
Lemon + milktop 15% of all pairs

Smell alikemoderate

Cooked together19,053 recipes

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

Smell alikelow

Cooked together106,462 recipes

Shared aroma: isobutyraldehyde (malty, green).
Lemon + flourtop 17% of all pairs

Smell alikemoderate

Cooked together30,404 recipes

Shared aroma: isobutyraldehyde (malty, green).

Flour and milk barely smell alike, yet cooks put them together in 78,219 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

Lemon: Provides the sharp acidity and bright aroma that define the custard's flavour.
Eggs: Yolks thicken the custard as they set, and whites whip into a stable meringue.
Sugar: Sweetens the custard to balance the lemon, and stabilises the whipped egg whites.
Flour: Thickens the lemon mixture so it sets into a sliceable custard rather than runny filling.
Milk: Adds moisture and body, carrying the flour into a smooth, soft custard.

The step that matters

Bake in a 350°F (175°C) oven until set. Egg proteins set as the custard heats, but overbaking tightens them too far, causing the filling to weep liquid, curdle, or turn rubbery. Pull it once the centre barely wobbles, since it will firm as it cools.