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Soup

Onion Soup

A creamy onion soup made with butter, water, milk, and rice flour.

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 the onions

  1. Scald, dry, and slice the onions.

  2. Sweat the onions in the melted butter.

Cook the soup

  1. Add the water, pepper, and salt, and cook until tender, about 2 hours.

  2. Rub the soup through a fine sieve and return it to a rinsed pan.

Thicken and finish

  1. Mix the rice flour with the milk until smooth, then add to the soup.

  2. Stir until the soup boils, then cook for 5 minutes.

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. Milk + ricetop 7% of all pairs
    Smell alikemoderate
    Cooked together7,374 recipes

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

  3. Onion + ricetop 9% of all pairs
    Smell alikemoderate
    Cooked together10,433 recipes

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

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

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

  5. Pepper + ricetop 12% of all pairs
    Smell alikemoderate
    Cooked together8,379 recipes

    Shared aroma: trans-2-nonenal (cardboard, fatty).

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

What each ingredient does

Spanish onions
Provide the main body and sweet flavour of the soup as they soften and break down.
Butter
Fat that gently sweats the onions and adds richness to the soup.
Rice flour
Thickens the soup as its starch swells when heated with liquid.
Milk
Adds creaminess and softness, and helps the flour mix in smoothly.

The step that matters

Mixing the rice flour with milk before adding it to the soup. Starch added directly to hot liquid clumps, because the outer layer hydrates before the inside does. Mixing it smoothly with cold milk first lets the starch disperse evenly, so it thickens the soup without lumps.

Swap the onion

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

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

Fit is the average pairing score against butter, pepper, milk, rice, flour. 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

French 31Brown 15with Milk 7White 5Bavarian 4Bermuda 4 See all 236 →

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