Sauce Albert — Horseradish Cream with English Mustard

Ingredients

• For the béchamel or velouté base
• 500 ml white béchamel or white velouté, freshly made, well-seasoned
• 150 ml heavy cream
• For the condiment trio
• 40 g fresh horseradish root, peeled and finely grated on a Microplane immediately before use; never jarred
• 1 tsp English mustard powder, dissolved in 1 tbsp cold water and rested 10 minutes before use
• 1 tbsp white wine vinegar
• to taste fine salt

Method

1. 1
   Mix the English mustard powder with one tablespoon of cold water in a small bowl. Set aside for 10 minutes undisturbed. The paste should smell sharp and acrid — this resting period develops the full sinigrin-derived pungency; a pale, weakly scented paste has not rested long enough.
2. 2
   Bring the béchamel or velouté to a gentle simmer in a heavy saucepan. Pour in the heavy cream and reduce over medium heat, stirring frequently, until the sauce is thick enough to coat a spoon cleanly and a finger drawn across the back leaves a clear, persistent line.
3. 3
   Remove the pan entirely from the heat. Stir in the white wine vinegar, then fold in the rested mustard paste and the freshly grated fresh horseradish. This is where the dish lives or dies: both horseradish's allyl isothiocyanate and mustard's sinigrin are volatile and heat-sensitive — any return to the heat, or any residual boiling, will drive off these compounds and leave a bland, cream-flavoured nothing. The finished sauce must never boil again.
4. 4
   Taste and season with fine salt. The sauce should deliver a sharp, almost floral nasal burn from the horseradish and a slow-building warmth from the mustard — if neither sensation is present, the sauce has been overheated and cannot be recovered. Serve within 2 minutes of adding the pungent elements.