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Spanish Onion Pie

A baked pie of sliced Spanish onions layered with butter, breadcrumbs, pepper, sea salt, and milk or gravy.

From an old cookbook · modernised transcription
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Why it works: Butter and milk are a kitchen classic. They rank in the top 7% of all ingredient pairs, and cooks put them together in 81,283 recipes. Both carry (z)-4-heptenal, which smells biscuit, cream. The science ↓

Spanish Onion 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

  1. Peel and slice the onions.

  2. Butter a pie dish and line it with breadcrumbs.

Layer and bake

  1. Add a layer of finely chopped onions, season with pepper and coarse sea salt, and add bits of butter.

  2. Continue layering with breadcrumbs and onions until the dish is full, finishing with a layer of breadcrumbs on top.

  3. Pour 1 cup of milk or gravy over the layers.

  4. Bake at 350°F (175°C) for 30 minutes.

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.

  1. Butter + milktop 7% of all pairs
    Smell alikemoderate
    Cooked together81,283 recipes

    Shared aroma: (z)-4-heptenal (biscuit, cream).

  2. Onion + peppertop 11% of all pairs
    Smell alikemoderate
    Cooked together68,474 recipes

    Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).

  3. Onion + buttertop 15% of all pairs
    Smell alikemoderate
    Cooked together42,912 recipes

    Shared aroma: decanal (soap, orange peel).

  4. Onion + milktop 20% of all pairs
    Smell alikemoderate
    Cooked together13,418 recipes

    Shared aroma: hexanal (green, grassy).

  5. Butter + peppertop 21% of all pairs
    Smell alikemoderate
    Cooked together85,593 recipes

    Shared aroma: trans-2-nonenal (cardboard, fatty).

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

What each ingredient does

Spanish onions
Form the bulk of the filling, softening and turning sweet as they bake.
Breadcrumbs
Soak up liquid and separate the onion layers, giving the pie a soft, structured texture.
Butter
Adds richness and fat that helps the onions brown lightly and taste rounder.
Milk or gravy
Provides moisture that soaks into the breadcrumbs and cooks the onions through.

Swap the onion

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

  1. Potatofits better
  2. Capsicumfits better
  3. Tomatofits about as well
  4. Onionthe original

Fit is the average pairing score against butter, pepper, 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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