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Onion Soup

A simple soup made with sliced onions, butter, flour, water, salt, pepper, and optional grated cheese.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 7 ingredients
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Why it works: Butter and cheese are a kitchen classic. They rank in the top 8% of all ingredient pairs, and cooks put them together in 7,962 recipes. Both carry delta-dodecalactone, which smells sweet, creamy. The science ↓

Onion Soup

Ingredients

Directions

Prepare

  1. Slice the onions thinly.

  2. In a pot, melt the butter over medium heat and add the onions.

Make the soup

  1. Cook until the onions are soft and golden, about 10 minutes.

  2. Sprinkle the flour over the onions and stir well.

  3. Add the water, salt, and pepper, then bring to a boil.

  4. Reduce heat and simmer for 30 minutes.

Serve

  1. Serve hot, topped with grated cheese if desired.

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 + cheesetop 8% of all pairs
    Smell alikemoderate
    Cooked together7,962 recipes

    Shared aroma: delta-dodecalactone (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 + cheesetop 16% of all pairs
    Smell alikemoderate
    Cooked together4,849 recipes

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

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 body and sweetness as they soften and turn golden.
Butter
Adds fat and richness and helps the onions brown gently.
Flour
Stirred into the onions to thicken the broth slightly.
Cheese
Optional topping that adds richness and savory flavor.

The step that matters

Cook the onions until soft and golden. Browning the onions slowly develops sweetness and depth of flavor. Rushing over high heat can scorch them, leaving a bitter taste that carries into the soup.

Swap the onion

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

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

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