2Whisk egg yolks in a small heavy saucepan until light lemon yellow and slightly thickened, about 1 minute. Whisk in1 to 1½ tablespoons lemon juice, depending on how tart you like your sauce.
3Add 2 tablespoons cold butter to egg mixture. Place the pan over very low heat and whisk constantly until butter melts and mixture thickens enough to see the bottom of the pan between strokes. (If the mixture starts to thicken too quickly or look grainy, remove it from the heat and whisk in 1 teaspoon cold water.)
