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A French Soup of Leeks

A soup made with leeks, butter, flour, milk, stock, and seasoned with parsley, salt, pepper, and egg yolk.

From an old cookbook · modernised transcription
From a historical cookbook (Internet Archive) · 10 ingredients
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Why it works: Parsley and pepper match in chemistry and in kitchens. They rank in the top 2% of all ingredient pairs, and cooks put them together in 34,122 recipes. Both carry 4'-methylacetophenone, which smells bitter almond. The science ↓

A French Soup of Leeks

Ingredients

Directions

Prepare and cook the leeks

  1. Trim and slice the leeks, discarding the green tops.

  2. In a saucepan, melt the butter and fry the leeks.

  3. Stir in the flour and cook for a minute.

Make the soup

  1. Add the hot milk and white stock, then season with parsley, salt, and pepper.

  2. Cook for 40 minutes.

  3. Remove from heat and stir in the egg yolk.

Serve

  1. Serve with croutons.

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. Parsley + peppertop 2% of all pairs
    Smell alikestrong
    Cooked together34,122 recipes

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

  2. Leek + parsleytop 4% of all pairs
    Smell alikestrong
    Cooked together759 recipes

    Shared aroma: trans-2-hexenal (green, leafy).

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

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

  4. Leek + flourtop 8% of all pairs
    Smell alikestrong
    Cooked together328 recipes

    Shared aroma: isobutyraldehyde (malty, green).

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

    Shared aroma: isobutyraldehyde (malty, green).

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

Leeks
Form the body of the soup and give it its mild, savoury flavour as they soften in butter.
Butter
Carries the frying of the leeks and adds richness to the soup.
Flour
Thickens the liquid into a smooth, body-rich soup once cooked briefly with the fat.
Milk
Adds creaminess and a soft, rounded texture to the soup.
Egg yolk
Enriches and thickens the soup slightly when stirred in off the heat.

The step that matters

Stir in the egg yolk off the heat. Egg yolk thickens by gentle heat; if the soup is still boiling when it goes in, the yolk can scramble and turn grainy instead of giving a smooth, silky texture.

Swap the leek

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

  1. Shallotfits about as well
  2. Chivefits about as well
  3. Potatofits about as well
  4. Leekthe original

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