Sauce Cardinal — Lobster Butter and Truffle Velouté

Ingredients

• For the lobster butter
• 200 g lobster shells, heads, claws, and walking legs, crushed
• 200 g unsalted butter, softened
• For the velouté base
• 500 ml fumet de poisson
• 30 g unsalted butter, for the roux
• 30 g plain flour, for the roux
• 100 ml lobster cooking liquor, concentrated broth from boiling or steaming lobster shells
• 60–80 g lobster butter, from above, cut into small pieces, cold
• 50 ml heavy cream
• 1 tbsp black truffle, brunoise, cut into 2 mm dice

Method

1. 1
   Make the lobster butter. Pound the crushed shells thoroughly with an equal weight of softened butter until well amalgamated. Transfer to a saucepan with a splash of water and melt gently — do not boil. Strain through a fine chinois, pressing firmly, into a bowl set over ice. Chill until the coral-red butter solidifies into a disc and can be lifted cleanly from any residual liquid. The butter is ready when it holds a firm, even colour with no visible shell fragments.
2. 2
   Make a blonde roux: melt 30 g butter in a heavy saucepan over moderate heat, add 30 g flour, and stir continuously until the paste smells faintly of cooked pastry but shows no colour. Add the fumet de poisson in stages, whisking to prevent lumps, and bring to a simmer. Skim and simmer for 20 minutes. The velouté is ready when it coats the back of a spoon and runs off in a slow, even sheet.
3. 3
   Add the 100 ml of lobster cooking liquor to the velouté and reduce by one-third over moderate heat, skimming as needed. The sauce deepens in body and marine character; it is ready when a spoon drawn across the surface leaves a momentary parting that closes slowly.
4. 4
   This is where the sauce lives or dies. Remove the pan from the heat entirely. Whisk in the lobster butter piece by piece — 60 to 80 g — working quickly so the residual heat melts each piece into emulsion before the next is added. If the pan is too hot the butter will break and the colour will turn orange rather than coral-pink; if too cold the butter will not incorporate. The finished sauce should be the colour of a faded rose: coral-pink with depth.
5. 5
   Stir in the 50 ml of heavy cream, then fold in the truffle brunoise. Pass the sauce through a fine chinois, pressing the truffle through or reserving the pieces to stir back in. Taste: lobster should register first, cream second, and truffle should linger as an afterthought. Adjust seasoning. The sauce is ready when no single element dominates and the aftertaste is musky and marine rather than sharp or flat.