First make the vinegar reduction. For this place the shallot, roughly-chopped bay leaf, peppercorns and white wine vinegar into a saucepan arid reduce until around 1 tablespoon of the liquid remains. Whilst reducing, place the egg yolks into a mixing bowl and whisk over a pan of simmering water until they thicken and leave a ribbon trail when mixing. Now remove from the heat and slowly add the melted, clarified butter (do this bit by bit), whilst whisking. Once the butter is added, sieve in the vinegar reduction. Check and season to taste.