1) Place your fish stock, shallots cracked pepper and vinegar in a thick bottom sauce pan.
2) Allow to reduce by half.
3) In the mean time, put your dices of butter in the freezer (or at least in the fridge) for 5 minutes. The butter has to be as cold as possible to ensure that the sauce does not split at the end.
4) When the reduction is ready, take your pot off the heat and whisk in all the butter in one go. At the end, the consistency of the sauce must be creamy. Season well with salt and pepper.
Some will strain the sauce before serving some would not. The choice is yours. Do not re-heat the sauce after wards, it would split.
If, you add a tablespoon of creme fraiche to your beurre blanc at the end, you will obtain a more stable sauce (it can be re-heated to a certain point, not to the boil thou!) and a beurre blanc called "a la Nantaise"
credits photo : beurre nantais et riz 4 © Jérôme Rommé
