(3/4 to 1 cup)
4 Tbsp butter
2 tsp prepared mustard, preferably Dijon
Juice of 1 lemon
Salt and freshly ground pepper to taste
2 tsp chopped parsley
1 tsp chopped chives
1/4 tsp grated nutmeg
4 egg yolks
In saucepan, combine butter, mustard, lemon juice, seasonings and herbs. Place the saucepand in a skillet containing simmering water (or use a double boiler) and stir with wire whisk until butter has melted.
Beat egg yolks until thick and lemon colored and stir them into the butter-mustard mixture. Continue beating vigorously over barely simmering water until sauce thickens.
Serve immediately over poached fish.