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Onion Soup

A soup made from onions, butter, flour, broth, toasted bread, and topped with cheese.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 8 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

  1. Peel and trim the ends of the onions, cut them in halves, and slice them finely.

Make the soup

  1. In a saucepan, melt the butter and fry the onions until light brown.

  2. Add the flour and cook for 5 minutes while stirring.

  3. Slowly add the hot broth or water and season with salt and pepper.

  4. Let it boil slowly for 20 minutes.

Serve

  1. Prepare the toasted bread with a thin slice of butter on each piece.

  2. Pour the soup into a tureen, cover to keep hot, and serve with grated cheese.

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. Butter + parmesan cheesetop 9% of all pairs
    Smell alikemoderate
    Cooked together4,163 recipes

    Shared aroma: guaiacol (smoky, sweet).

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

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

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

    Shared aroma: isobutyraldehyde (malty, green).

  5. Pepper + parmesan cheesetop 14% of all pairs
    Smell alikemoderate
    Cooked together5,322 recipes

    Shared aroma: ethyl 2-methylbutyrate (fruity, apple).

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
Sweetness and savoury depth as they brown in the butter.
Butter
Fat that carries the onion flavour and helps them brown.
Flour
Thickens the broth into a body-rich soup as it cooks.
Broth or water
Forms the liquid base that the soup simmers in.

The step that matters

Frying the onions until light brown. Onions cooked slowly until golden develop sweet, deep flavour through browning. Pale or burnt onions change the final taste of the soup noticeably.

Swap the onion

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

  1. Asparagusfits better
  2. Spinachfits better
  3. Tomatofits better
  4. Onionthe original

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

More onion soup recipes

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

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