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Onion Sauce

A brown onion sauce made with butter, flour, gravy, salt, white pepper, and optional lemon juice.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 7 ingredients
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Why it works: Flour and butter are a kitchen classic. They rank in the top 12% of all ingredient pairs, and cooks put them together in 124,287 recipes. Both carry isobutyraldehyde, which smells malty, green. The science ↓

Onion Sauce

Ingredients

Directions

Prepare the onions

  1. Peel and finely slice the onions.

Make the sauce

  1. In a saucepan, melt the butter and gently stir in the onions until they are light brown.

  2. Sprinkle the flour over the onions and mix well.

  3. Add the gravy and let it simmer gently until the onions are tender.

  4. Rub the mixture through a fine sieve and return it to the saucepan.

  5. Season with salt and white pepper to taste.

  6. If the sauce is too thin, boil it quickly to reduce.

Finish and serve

  1. Add a few drops of lemon juice just before serving.

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

    Shared aroma: isobutyraldehyde (malty, green).

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

    Shared aroma: decanal (soap, orange peel).

  3. Butter + lemontop 16% of all pairs
    Smell alikemoderate
    Cooked together41,227 recipes

    Shared aroma: 3-hexenal (apple, fruity).

  4. White pepper + lemontop 16% of all pairs
    Smell alikelow
    Cooked together1,658 recipes

    Shared aroma: eucalyptol (eucalyptus, herbal).

  5. Flour + lemontop 17% of all pairs
    Smell alikemoderate
    Cooked together30,404 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, savoury flavour of the sauce as they soften and brown.
Flour
Thickens the sauce as it cooks with the butter and liquid.
Butter
Carries flavour and adds richness while the onions brown.
Good gravy
Supplies the liquid and savoury depth that the onions cook into.

The step that matters

Browning the onions in the butter. Onions that are only pale or that brown unevenly give a flat, bitter-edged flavour. Gentle, even browning builds sweetness through caramelisation, so stir steadily over moderate heat.

Swap the white pepper

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

  1. Parsleyfits better
  2. Capersfits better
  3. Thymefits better
  4. White pepperthe original

Fit is the average pairing score against onion, flour, butter, lemon. 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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