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Onion Soup

A creamy soup made from onions, butter, flour, milk, mashed potato, and seasoned with pepper, salt, celery essence, served over fried bread.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 11 ingredients
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Why it works: Onion and potato are a kitchen classic. They rank in the top 3% of all ingredient pairs, and cooks put them together in 9,023 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓

Onion Soup

Ingredients

Directions

Make the soup base

  1. Fry the onions in the butter until soft.

  2. Strain the butter and return it to the frying pan.

  3. Gradually stir in the flour and cook until it turns light brown.

  4. Slowly add the boiling water to thin the mixture.

  5. Heat the milk and mix it into the mashed potato gradually.

  6. Strain the potato mixture through a colander into a saucepan.

  7. Add the baking soda and set the saucepan in a pot of boiling water.

  8. Cook for ten minutes, seasoning with pepper and salt.

Finish and serve

  1. Stir in the fried onions and essence of celery.

  2. Let the soup stand in hot water for ten minutes.

  3. Serve over the diced fried bread in a tureen.

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. Onion + potatotop 3% of all pairs
    Smell alikemoderate
    Cooked together9,023 recipes

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

  2. Pepper + celerytop 5% of all pairs
    Smell alikestrong
    Cooked together16,012 recipes

    Shared aroma: 4'-methylacetophenone (bitter almond).

  3. Potato + celerytop 7% of all pairs
    Smell alikemoderate
    Cooked together2,047 recipes

    Shared aroma: 4'-methylacetophenone (bitter almond).

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

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

  5. Butter + milktop 7% of all pairs
    Smell alikemoderate
    Cooked together81,283 recipes

    Shared aroma: (z)-4-heptenal (biscuit, cream).

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

What each ingredient does

Onions
Softened in butter, they supply the soup's sweet, savory flavor base.
Flour
Cooked with butter and thinned with water, it thickens the soup into a smooth body.
Milk
Adds creaminess and richness to the soup's texture.
Mashed potato
Adds body and helps thicken the soup further.
Baking soda
Raises the soup's pH, which can darken and soften the mixture.

The step that matters

Adding the baking soda to the hot potato mixture. Baking soda is strongly alkaline, so only a pea-sized amount should be used. Too much can leave a soapy taste and an off color in the finished soup.

Swap the celery

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

  1. Parsleyfits better
  2. Garlicfits better
  3. Thymefits about as well
  4. Celerythe original

Fit is the average pairing score against onion, butter, flour, milk, potato, 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.

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