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Sauce

Brown Onion Sauce

A savory sauce made from sliced onions, butter, gravy, port wine, and mushroom ketchup.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 9 ingredients
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Why it works: Butter and mushroom are a kitchen classic. They rank in the top 7% of all ingredient pairs, and cooks put them together in 12,525 recipes. Both carry trans-2-decenal, which smells waxy, orange. The science ↓

Brown Onion Sauce

Ingredients

Directions

Prepare the onions

  1. Slice the large Spanish onions.

  2. In a frying pan, melt a bit of butter over low heat.

  3. Add a few onion slices at a time, browning them slowly.

  4. As they shrink and brown, add more slices until all are in the pan.

Make the sauce

  1. Season with coarse sea salt, black pepper, and a dust of cayenne.

  2. Add ½ cup of rich brown gravy and a piece of butter rolled in flour.

  3. Let it simmer until the onions are tender and the sauce is smooth.

  4. Skim if necessary, then stir in ⅓ cup of port wine and ⅓ cup of mushroom ketchup.

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 + mushroomtop 7% of all pairs
    Smell alikemoderate
    Cooked together12,525 recipes

    Shared aroma: trans-2-decenal (waxy, orange).

  2. Onion + mushroomtop 10% of all pairs
    Smell alikemoderate
    Cooked together10,626 recipes

    Shared aroma: 2,4-decadienal (seaweed).

  3. Port wine + mushroomtop 10% of all pairs
    Smell alikemoderate
    Cooked together570 recipes

    Shared aroma: guaiacol (smoky, sweet).

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

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

  5. Pepper + mushroomtop 11% of all pairs
    Smell alikemoderate
    Cooked together13,580 recipes

    Shared aroma: 2-nonenal (fatty, green).

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

What each ingredient does

Spanish onions
Slow browning caramelises their natural sugars, giving the sauce its deep colour and sweet flavour.
Butter
Fat that carries the onions' browning and adds richness to the sauce.
Butter rolled in flour
Flour thickens the sauce as it simmers, giving it a smooth body.
Rich brown gravy
Provides the liquid base and savoury depth of the sauce.
Port wine
Adds sweetness and fruity depth that rounds out the savoury onions.
Mushroom ketchup
Adds concentrated savoury umami flavour to the sauce.

The step that matters

Browning the onions slowly over low heat. Onions brown through caramelisation, which needs gentle, sustained heat. Rushing with high heat scorches the sugars before the onions soften and sweeten, leaving a bitter taste instead of a deep, rich one.

Swap the onion

How well each one fits the dish's main ingredients (butter, pepper, flour, port wine, mushroom, ketchup):

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

Fit is the average pairing score against butter, pepper, flour, port wine, mushroom, ketchup. 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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