Name: Sauce Robert.—Robert Sauce
Ingredients: 2 tablespoons flour; 3 large onions, finely minced; 2 tablespoons butter; 2 cups stock; ¼ teaspoon coarse sea salt; ¼ teaspoon black pepper; 1 teaspoon vinegar; 1 teaspoon mustard

Why it works: Onion and mustard match in chemistry and in kitchens. They rank in the top 6% of all ingredient pairs, and cooks put them together in 9,259 recipes. Both carry 2-isopropyl-3-methoxypyrazine, which smells earthy, pea. The science ↓

Sauce Robert.—Robert Sauce

Ingredients

Directions

Make the sauce

In a stewpan, heat the flour over medium heat until it turns a brownish color.
Add the minced onions and butter, frying until the onions are browned.
Pour in the stock, skimming occasionally, and let the sauce boil for 30 minutes.

Finish and serve

Before serving, stir in the salt, pepper, vinegar, and mustard.

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.

Onion + mustardtop 6% of all pairs

Smell alikestrong

Cooked together9,259 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Vinegar + mustardtop 7% of all pairs

Smell alikemoderate

Cooked together14,067 recipes

Shared aroma: isobutyraldehyde (malty, green).
Pepper + mustardtop 9% of all pairs

Smell alikemoderate

Cooked together15,430 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Onion + peppertop 11% of all pairs

Smell alikemoderate

Cooked together68,474 recipes

Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
Flour + buttertop 12% of all pairs

Smell alikelow

Cooked together124,287 recipes

Shared aroma: isobutyraldehyde (malty, green).

Flour and butter 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

Flour: Browned in the pan first, it thickens the stock and adds a nutty, toasted flavor.
Onions: Frying until browned builds sweetness and deep savory flavor for the sauce.
Butter: Carries the frying of the onions and adds richness and fat to the sauce.
Stock: Forms the liquid base that the flour thickens during the long boil.
Vinegar: Adds a sharp acidity that brightens the rich, savory sauce.
Mustard: Adds a sharp, pungent note that rounds out the sauce's flavor.

The step that matters

Browning the flour. Heating the flour until it turns brownish is what gives the sauce its color and toasted flavor. Cooking it too briefly leaves a raw, pasty taste, while cooking it too far can turn it bitter.

Swap the onion

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

Shallotfits better
Horseradishfits better
Radishfits better
Onionthe original

Fit is the average pairing score against flour, butter, pepper, vinegar, mustard. 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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Sauce Robert.—Robert Sauce