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Onion Soup Au Gratin

A baked onion soup topped with toasted bread and 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 Au Gratin

Ingredients

Directions

The book gives no oven temperature. The 400°F (200°C) in the steps was added when the recipe was transcribed, as a starting point.

Prepare the soup

  1. Prepare and strain 4 cups of consomme and keep it hot.

  2. Slice 3 onions and brown them in 1 tablespoon of butter for 15 minutes.

  3. Stir in 3 tablespoons of flour and ¼ teaspoon of cayenne pepper.

  4. Add the hot consomme and let it simmer for 85 minutes.

Bake and serve

  1. Pour the soup into an earthen soup tureen.

  2. Place G slices of toast on top and dust with 3 ounces of cheese.

  3. Bake in a 400°F (200°C) oven for 15 minutes.

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
Browned slowly in butter to build sweetness and deep savory flavor for the soup.
Flour
Thickens the soup as it cooks with the consomme, giving it body.
Cheese
Melts and browns on top of the toast, forming the gratin crust.
Consomme
Provides the main liquid and savory beef-style base of the soup.

The step that matters

Browning the onions. Onions need enough time over moderate heat to caramelize fully; rushing leaves them pale and bitter-tasting, and the soup's depth depends on this sweetness.

Swap the onion

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

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

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