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Onion Soup

A savory soup made with onions, butter, water, milk, flour, pepper, and sea salt, served with toasted bread.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 7 ingredients
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Why it works: Butter and milk 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 Soup

Ingredients

Directions

Prepare

  1. Peel and finely chop the onions.

  2. In a saucepan, melt the butter and fry the onions for five minutes without browning.

Make the soup

  1. Add the hot water, season with pepper and salt, and boil for twenty minutes until the onions are tender.

  2. Blend the flour with the milk, then strain it into the soup.

  3. Boil for five minutes to cook the flour.

Serve

  1. Serve with toasted bread.

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 + milktop 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. Onion + buttertop 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

Onions
Provide the main flavour and body of the soup as they soften and sweeten.
Butter
Carries the onions' flavour and adds richness while frying them gently.
Flour
Thickens the soup so it has a smooth, body-rich texture once fully cooked.
Milk
Adds creaminess and softness to the soup, mellowing its flavour.

The step that matters

Frying the onions without browning. Gentle frying softens the onions and draws out their sweetness; browning would add bitter, toasted notes that change the soup's clean flavour.

Swap the onion

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

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

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

More onion soup recipes

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