In a small heavy saucepan or double boiler, whisk the egg yolks, water and lemon juice. Cook and stir over low heat or simmering water until mixture bubbles around edges and reaches 160°, about 20 minutes.
Cut cold butter into eight pieces; add to yolk mixture, one piece at a time, stirring after each addition until melted. Stir in the salt, paprika and pepper. Serve immediately.
Editor’s Note:Sauce Mousseline: Prepare as directed. Gently fold in 1/2 cup whipped cream. Yield: 1-1/3 cups. Ancho Chili Sauce: Prepare as directed, except decrease lemon juice to 1/2 teaspoon. Stir in 1/2 to 1 teaspoon ground ancho chili pepper and 1/4 teaspoon ground cumin. Yield: 1 cup.