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Baked Onions

Baked onions are onions cooked in a sauce of butter, flour, and milk, topped with buttered breadcrumbs and baked until golden.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 9 ingredients
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Why it works: Butter and bread 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 ↓

Baked Onions

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. Boil the onions in three salted waters until tender.

  2. Place the boiled onions in a baking dish.

Make the sauce

  1. In a saucepan, melt the butter and stir in the flour to make a roux.

  2. Gradually add the hot milk while stirring continuously until smooth.

  3. Season the sauce with salt and pepper.

Bake and serve

  1. Pour the sauce over the onions.

  2. Cover the dish with buttered bread crumbs.

  3. Bake at 400°F (200°C) until the crumbs are brown.

  4. Serve in the same dish with a napkin folded diagonally around it.

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 + breadtop 7% of all pairs
    Smell alikemoderate
    Cooked together27,232 recipes

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

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

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

  3. Milk + breadtop 11% of all pairs
    Smell alikemoderate
    Cooked together11,466 recipes

    Shared aroma: 2-undecenal (sweet).

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

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

  5. Flour + buttertop 12% of all pairs
    Smell alikelow
    Cooked together124,287 recipes

    Shared aroma: isobutyraldehyde (malty, green).

Flour and butter barely smell alike, yet cooks put them together in 124,287 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

Onions
Provide the main body and sweet, soft flesh of the dish after boiling until tender.
Butter
Enriches the sauce with fat and helps the crumbs brown in the oven.
Flour
Thickens the milk into a smooth sauce when cooked with the butter as a roux.
Milk
Forms the creamy base of the sauce that coats the onions.
Bread crumbs
Form a golden crust on top when baked, adding texture contrast.

The step that matters

Adding the hot milk to the roux. Adding milk gradually while stirring constantly keeps the flour dispersed, so the sauce becomes smooth rather than lumpy.

Swap the onion

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

  1. Capsicumfits better
  2. Potatofits better
  3. Shallotfits better
  4. Onionthe original

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