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Onion Sauce

A creamy sauce made from boiled onions, milk, butter, and flour.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 6 ingredients
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Why it works: Milk and butter 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 ↓

Onion Sauce

Ingredients

Directions

Prepare the onions

  1. Peel the onions and place them in cold water.

  2. Bring the onions to a boil, then strain.

  3. Return the onions to the saucepan.

  4. Add ¼ teaspoon of salt and enough boiling water to cover them.

  5. Boil until tender (about 1 hour).

  6. Drain and chop the onions coarsely.

Make the sauce

  1. Melt the butter in a saucepan.

  2. Stir in the flour and cook for 2-3 minutes.

  3. Add the milk and stir until it boils.

  4. Add the chopped onions.

  5. Season to taste.

  6. Simmer for a few minutes.

  7. Serve.

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. Milk + buttertop 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. Butter + flourtop 12% of all pairs
    Smell alikelow
    Cooked together124,287 recipes

    Shared aroma: isobutyraldehyde (malty, green).

  4. Milk + flourtop 14% of all pairs
    Smell alikelow
    Cooked together78,219 recipes

    Shared aroma: isobutyraldehyde (malty, green).

  5. Butter + oniontop 15% of all pairs
    Smell alikemoderate
    Cooked together42,912 recipes

    Shared aroma: decanal (soap, orange peel).

Butter and flour 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

Butter
Adds fat and richness, and carries flavour into the sauce.
Flour
Thickens the milk into a smooth sauce as its starch swells when heated.
Milk
Forms the liquid base of the sauce, giving it body and a mild, creamy taste.
Onions
Provide the main flavour and, once softened and chopped, bulk and texture to the sauce.

The step that matters

Stir in the flour and cook for 2-3 minutes. Cooking the flour in melted butter for a few minutes cooks off its raw starch taste and lets it thicken evenly. Skipping this, or adding milk too early, can leave lumps and a pasty flavour.

Swap the onion

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

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

Fit is the average pairing score against milk, butter, flour, 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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