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Onion Soup

A soup made from sliced onions, butter, flour, milk, water, potato, and sweet cream.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 8 ingredients
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Why it works: Onion and potato are a kitchen classic. They rank in the top 3% of all ingredient pairs, and cooks put them together in 9,023 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓

Onion Soup

Ingredients

Directions

  1. Fry the sliced onions in butter until brown.

  2. Stir in the flour and mix well.

  3. Add the milk and water slowly, then season to taste.

  4. Incorporate the grated potato and cook in a kettle of boiling water for 10 minutes.

  5. Stir in the sweet cream and serve immediately.

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 + potatotop 3% of all pairs
    Smell alikemoderate
    Cooked together9,023 recipes

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

  2. Butter + milktop 7% of all pairs
    Smell alikemoderate
    Cooked together81,283 recipes

    Shared aroma: (z)-4-heptenal (biscuit, cream).

  3. Butter + creamtop 8% of all pairs
    Smell alikemoderate
    Cooked together41,516 recipes

    Shared aroma: delta-dodecalactone (sweet, creamy).

  4. Milk + potatotop 9% of all pairs
    Smell alikemoderate
    Cooked together3,611 recipes

    Shared aroma: (e,z)-2,6-nonadienal (cucumber, melon).

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

    Shared aroma: isobutyraldehyde (malty, green).

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

Onions
Frying until brown builds a deep, sweet, caramelized flavour as the base of the soup.
Flour
Stirred into the butter and onions, it thickens the milk and water into a smooth body.
Milk
Forms the creamy liquid base of the soup, adding richness and mild sweetness.
Grated potato
Releases starch as it cooks, helping the soup thicken and become more velvety.
Sweet cream
Stirred in at the end, it adds fat and richness that smooth out the finished soup.

The step that matters

Frying the onions until brown. Onions that are only softened stay pale and mild. Cooking them until deeply browned develops sweet, savoury flavour through caramelisation, which sets the character of the whole soup.

Swap the onion

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

  1. Chivefits better
  2. Leekfits better
  3. Asparagusfits about as well
  4. Onionthe original

Fit is the average pairing score against butter, flour, milk, potato, cream. 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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