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Onion Soup

A simple soup made with sliced onions, butter, flour, and boiling water, served with bread and butter.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 7 ingredients
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Why it works: Butter and bread are a kitchen classic. They rank in the top 7% of all ingredient pairs, and cooks put them together in 27,232 recipes. Both carry delta-decalactone, which smells sweet, creamy. The science ↓

Onion Soup

Ingredients

Directions

Prepare the soup

  1. Slice the onions and blanch them in boiling water.

  2. In a 2-quart saucepan, melt the butter over medium heat.

  3. Add the onions and stir until they are light brown.

  4. Thicken the mixture with flour and stir for 2-3 minutes.

  5. Add the boiling water, salt, and pepper, and stir until it boils.

  6. Let the soup simmer for 5-10 minutes.

Serve

  1. In a soup tureen, place a few slices of dried bread and 1 ounce of butter.

  2. Pour the soup gently into the tureen, stirring to dissolve the butter.

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 + breadtop 7% of all pairs
    Smell alikemoderate
    Cooked together27,232 recipes

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

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

    Shared aroma: decanal (soap, orange peel).

  5. Onion + breadtop 15% of all pairs
    Smell alikemoderate
    Cooked together8,676 recipes

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

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
Browning in the butter builds sweetness and deep savory flavor in the soup.
Butter
Carries the onions as they cook and adds richness to the finished soup.
Flour
Thickens the soup broth so it has body rather than being watery.

The step that matters

Browning the onions. Onions need enough time over medium heat to turn light brown, which develops sweetness and flavor. Stopping early leaves the soup flat, while stirring too little can scorch them.

Swap the onion

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

  1. Shallotfits better
  2. Capsicumfits better
  3. Leekfits better
  4. Onionthe original

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