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Onions Au Gratin

A baked dish of sliced onions layered with bread crumbs, butter, salt, pepper, and grated cheese.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 6 ingredients
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Why it works: Bread and butter are a kitchen classic. They rank in the top 7% of all ingredient pairs, and cooks put them together in 27,232 recipes. Both carry delta-decalactone, which smells sweet, creamy. The science ↓

Onions Au Gratin

Ingredients

Directions

The book gives no oven temperature. The 400°F (200°C) in the steps was added when the recipe was transcribed, as a starting point.

Prepare the onions

  1. Cut the onions into thick slices.

  2. Parboil the slices in salted water.

Assemble and bake

  1. Layer the onions in a casserole with bread crumbs, salt, pepper, and bits of butter.

  2. Top with a layer of bread crumbs mixed with grated cheese.

  3. Bake in a 400°F (200°C) oven until browned.

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. Bread + buttertop 7% of all pairs
    Smell alikemoderate
    Cooked together27,232 recipes

    Shared aroma: delta-decalactone (sweet, creamy).

  2. Bread + cheesetop 7% of all pairs
    Smell alikemoderate
    Cooked together2,130 recipes

    Shared aroma: delta-decalactone (sweet, creamy).

  3. Butter + cheesetop 8% of all pairs
    Smell alikemoderate
    Cooked together7,962 recipes

    Shared aroma: delta-dodecalactone (sweet, creamy).

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

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

  5. Onion + buttertop 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

Large onions
Form the main body of the dish, becoming soft and sweet as they cook.
Bread crumbs
Add a crisp, golden topping and absorb moisture as the dish bakes.
Butter
Adds richness and helps the crumbs and onions brown in the oven.
Grated cheese
Melts into the crumbs and browns, adding savory flavor and a golden crust.

The step that matters

Bake until browned. Onions and cheese need enough oven heat to brown properly. Underbaking leaves the topping pale and the onions watery, while the Maillard reaction gives the golden color and flavor.

Swap the onion

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

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

Fit is the average pairing score against bread, pepper, butter, cheese. 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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