Despite its high price, Dover sole is one of the best-selling fish on restaurant menus. It’s perfect if you want something simple, light and clean to eat, but do expect to pay double what you would for a portion of normal fish.
First make the béarnaise sauce: place the vinegar, shallot, herbs and peppercorns in a saucepan with 3tablespoons of water and reduce the liquid by boiling for a few minutes until there is no more than a dessertspoonful. Strain through a sieve and leave to cool.