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 ↓
Brown Onion Sauce—-piquant
Ingredients
Directions
Make the onion base
In a saucepan, melt the butter over medium heat.
Add the chopped onions and fry them lightly.
Pour in the vinegar and let it reduce to one third.
Stir in the mustard flour until well mixed.
Finish the sauce
Slowly add the veal gravy and Espagnole sauce while stirring.
Let the mixture boil slowly for 25 minutes.
Season with salt and pepper, then strain through a fine sieve.
Keep warm until ready to serve.
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.
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Onion + mustardtop 6% of all pairsSmell alikestrongCooked together9,259 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Vinegar + mustardtop 7% of all pairsSmell alikemoderateCooked together14,067 recipes
Shared aroma: isobutyraldehyde (malty, green).
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Mustard + peppertop 9% of all pairsSmell alikemoderateCooked together15,430 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Onion + peppertop 11% of all pairsSmell alikemoderateCooked together68,474 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Butter + flourtop 12% of all pairsSmell alikelowCooked 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
- Red onions
- Provide the main body and sweet, savoury flavour of the sauce as they soften and brown.
- Butter
- Adds fat for gentle frying and a rich, rounded mouthfeel to the sauce.
- Vinegar
- Adds acidity that balances the sweetness of the onions and sharpens the finished sauce.
- Mustard flour
- Contributes pungent flavour and helps thicken the sauce as it is stirred in.
- Veal gravy
- Supplies meaty depth and savoury body to the sauce.
- Espagnole sauce
- Adds a concentrated, roasted base that gives the sauce body, colour and richness.
The step that matters
Reducing the vinegar to one third. Reducing concentrates the acid and flavour so the sharpness is balanced. If it is under-reduced the sauce tastes thin and sour, and if over-reduced it can turn harsh and sticky before the gravy is added.
Swap the onion
How well each one fits the dish's main ingredients (butter, vinegar, mustard, flour, veal, sauce, pepper):
- Shallotfits better
- Horseradishfits better
- Capsicumfits better
- Onionthe original
Fit is the average pairing score against butter, vinegar, mustard, flour, veal, sauce, pepper. 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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