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Brown Onion Soup

A soup made from browned onions, boiled in water, seasoned with pepper and salt, thickened with penny loaf crumbs, finished by egg yolk and vinegar.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 9 ingredients
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Why it works: Pepper and clove match in chemistry and in kitchens. They rank in the top 5% of all ingredient pairs, and cooks put them together in 17,451 recipes. Both carry ethyl octanoate, which smells fruity, wine. The science ↓

Brown Onion Soup

Ingredients

Directions

Prepare the onions

  1. Skin and slice the onions.

  2. Fry the onions in butter until brown and tender.

  3. Drain the onions on a sieve to remove excess butter.

Make the soup

  1. In a pot, combine the drained onions with boiling water and boil for 1 hour, stirring often.

  2. Add pepper and salt to taste.

  3. Rub the crumbs of the penny loaf through a colander and add to the soup, stirring well to avoid lumps.

  4. Boil for an additional 2 hours.

  5. Add cloves if desired.

Finish and serve

  1. Ten minutes before serving, beat the egg yolks with vinegar and a little soup, then gradually stir it into the pot while stirring continuously.

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. Pepper + clovetop 5% of all pairs
    Smell alikestrong
    Cooked together17,451 recipes

    Shared aroma: ethyl octanoate (fruity, wine).

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

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

  3. Onion + clovetop 13% of all pairs
    Smell alikemoderate
    Cooked together16,901 recipes

    Shared aroma: 2-nonanone (fruity, floral).

  4. Onion + vinegartop 14% of all pairs
    Smell alikemoderate
    Cooked together18,226 recipes

    Shared aroma: acetic acid (sour, vinegar).

  5. Pepper + vinegartop 14% of all pairs
    Smell alikemoderate
    Cooked together27,814 recipes

    Shared aroma: 4'-methylacetophenone (bitter almond).

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

What each ingredient does

Spanish onions
Form the bulk of the soup and, when fried until brown, give it its deep, sweet flavour.
Butter
Fat for frying the onions, helping them brown and develop rich flavour.
Penny loaf crumbs
Bread that thickens the soup as it is rubbed in and boiled.
Egg yolks
Enrich the soup and thicken it gently when stirred in off the heat.
Vinegar
Adds a little acidity that brightens the sweet, rich onion flavour.

The step that matters

Adding the egg yolks. Egg yolks can curdle or scramble if they meet hot liquid too quickly. Beating them with vinegar and some hot soup first, then stirring gradually and constantly, tempers them so they thicken the soup smoothly.

Swap the clove

The recipe marks clove as optional. How well each one fits the dish's main ingredients (onion, butter, pepper, egg, vinegar):

  1. Parsleyfits better
  2. Tarragonfits better
  3. Garlicfits better
  4. Clovethe original

Fit is the average pairing score against onion, butter, pepper, egg, vinegar. 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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