White butter sauce -  Sauce blanche

White Butter Sauce  Beurre Blanc

Ingredients

10cl white vinegar
10cl white wine ( muscadet, Sauvignon Blanc or any drinkable dry white wine. 
For a luxurious beurre blanc, try making the sauce with Champagne :)
10 small shallots finely chopped
2 tbsp. of fresh cream
500g butter cold
Salt and pepper
Quartered lemons

Method

1. Cut the butter into medium cubes and return the butter cubes to the fridge to keep them cold while the liquid is reducing.
   
2. Heat wine, vinegar and chopped shallots in a saucepan until the liquid boils, then lower the heat and continue simmering until the liquid has reduced down to about 1 tbsp. (nearly dry). This should take 10 to 15 minutes.
   
3. It is now time to continue the sauce in a Bain-Marie (see link)
   
4. Add the fresh cream.
   
5. Return to the boil
   
6. Once the wine-vinegar-shallots has reduced, reduce the heat to low and add the cold cubes of butter and whisk rapidly with a wire whisk if you do have one or just a wooden spoon. Keep the low heat at all time
   
7. Continue whisking until the butter is totally melted and incorporated. The finished sauce should be thick and smooth.
   
8. Season to taste.
   
9. Wrap the cooked seafood with the sauce and serve right away with lemon wedges on the side to squeeze over the seafood.
   

You can keep the sauce warm by keeping the saucepan in the bain-marie on the back burner, on very low heat, while you cook the meat.
The traditional recipe sauce does not have fresh cream, but the trick for the sauce to be stable is to introduce fresh cream.