Béarnaise Sauce

Method

1. Melt 60 g of unsalted butter in a small pan over the lowest heat without stirring, about 5 minutes. Skim the white foam from the surface, then pour the clear golden fat carefully into a small jug, leaving the milky solids in the bottom of the pan. Set the clarified butter aside somewhere warm, around 50C — it must not be hot enough to scramble the yolk.
2. Put 1 small shallot, finely chopped, into a small stainless steel or enamelled pan with 2 tbsp of white wine vinegar, 2 tbsp of dry white wine, 4 coarsely crushed black peppercorns and the reserved tarragon stalks. Bring to a simmer over medium heat and reduce for 5-6 minutes, until only about 1 tbsp of syrupy liquid remains.
3. Strain the reduction through a fine sieve into a heatproof bowl, pressing the shallot and stalks well to extract every drop, then leave it to cool for 2 minutes until just warm.