Why it works: Parsley and pepper match in chemistry and in kitchens. They rank in the top 2% of all ingredient pairs, and 34,122 recipes mention both. Both carry 4'-methylacetophenone, which smells bitter almond. The science ↓
Tartar Sauce— No. 2
Ingredients
Directions
In a mortar, combine minced onions, parsley, dry mustard, salt, pepper, and hard-boiled egg yolks, then pound the ingredients until smooth.
Transfer to a bowl and gradually mix in the salad oil, starting with drops and then adding teaspoonfuls while beating well between each addition to prevent curdling.
Once the oil is fully incorporated, add the best vinegar and chili vinegar.
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 aroma chemistry they share, and how many recipes mention both.
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Parsley + peppertop 2% of all pairsAroma overlapstrongMentioned together34,122 recipes
Shared aroma: 4'-methylacetophenone (bitter almond).
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Onion + mustardtop 6% of all pairsAroma overlapstrongMentioned together9,259 recipes
Shared aroma: 2-isopropyl-3-methoxypyrazine (earthy, pea).
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Mustard + vinegartop 7% of all pairsAroma overlapmoderateMentioned together14,067 recipes
Shared aroma: isobutyraldehyde (malty, green).
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Parsley + mustardtop 8% of all pairsAroma overlapstrongMentioned together2,588 recipes
Shared aroma: trans-2-hexenal (green, leafy).
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Onion + parsleytop 9% of all pairsAroma overlapmoderateMentioned together25,843 recipes
Shared aroma: 2,4-decadienal (seaweed).
Ranks compare each pair with 20,000 random ingredient pairs on CompKitchen. How we score pairs
What each ingredient does
- Hard-boiled egg yolks
- Emulsify the oil into the sauce, giving it a thick, creamy body.
- Salad oil
- Provides fat that gives the sauce its rich, smooth texture.
- Dry mustard
- Adds sharp flavour and helps stabilise the emulsion.
- Best vinegar
- Adds acidity that brightens the rich oil and egg.
The step that matters
Adding the oil gradually. Oil added too fast cannot be absorbed by the egg yolk and mustard, so the emulsion breaks and the sauce curdles. Adding it in drops first, then teaspoonfuls, while beating between additions, lets the yolk coat each droplet and keeps the sauce smooth and thick.
Flavor stand-ins for the onion
How well each one fits the dish's main ingredients (parsley, mustard, pepper, egg, vinegar):
- Horseradishbetter flavor fit
- Shallotbetter flavor fit
- Lettucebetter flavor fit
- Onionthe original
Fit is the average pairing score against parsley, mustard, pepper, egg, vinegar. Candidates are from the same food group and used in at least 100 recipes. This compares flavor only: it does not check the job the ingredient does in the dish (bulk, moisture, acidity, structure).
“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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