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Baked Spanish Onion

A dish of onions baked until blackened, then seasoned with butter, pepper, and coarse sea salt.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 4 ingredients
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Why it works: Onion and pepper are a kitchen classic. They rank in the top 11% of all ingredient pairs, and cooks put them together in 68,474 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓

Baked Spanish Onion

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.

Bake the onions

  1. Preheat the oven to 400°F (200°C).

  2. Place the onions in a pan and bake for 4 hours until the outside is blackened and they begin to shrink.

  3. Test for tenderness with a knitting needle.

Finish and serve

  1. Once tender, remove the skin from the onions.

  2. Top with a little butter, pepper, and coarse sea salt.

  3. Return to the oven for a few more 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. Onion + peppertop 11% of all pairs
    Smell alikemoderate
    Cooked together68,474 recipes

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

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

    Shared aroma: decanal (soap, orange peel).

  3. 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

Onions
Slow baking softens the flesh and concentrates sweetness as the outside blackens and shrinks.
Butter
Adds fat that carries flavour and gives the softened onion a rich, silky finish.

The step that matters

Testing for tenderness before removing the skin. Onions cooked too briefly stay firm in the centre, while over-baking dries them out. Checking with a knitting needle confirms the interior has softened fully before the skin is removed and the onions are finished.

Swap the onion

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

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

Fit is the average pairing score against butter, pepper. 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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