Combine egg yolks and lemon juice in blender. Melt butter and heat until it bubbles--don't brown. Add 1 tablespoon hot water to egg yolks and lemon juice; turn blender on high speed in immediately pour in hot butter in a steady stream. (this takes about 5 seconds.)
Add salt, red pepper, and mustard; Blend until well blended-about 30 seconds.
Makes about 2 cups of sauce.
HOLLANDAISE WITH CUCUMBER OR SHRIMP: Either of these variations is good with fish. After you have made the sauce, stir it into 1 tablespoon each chopped parsley and chives. Then add either one cucumber (peeled, seeded, and chopped) or one can (about 5 ounces) shrimp, which have been rinsed and drained.