Step 1 Stovetop Method: Whisk egg yolks in glass or stainless steel bowl until frothy. Whisk in lemon juice, cayenne pepper and salt. Set bowl over saucepan containing about 1-1/2 inches (4 cm) simmering water. (Bottom of bowl should not touch water.) Heat, whisking constantly, until egg mixture turns pale yellow, thickens slightly and increases in volume. Remove from heat. Slowly whisk in melted butter until sauce is smooth and thickened. Serve warm.
Step 2 Microwave Method: Whisk egg yolks, lemon juice, cayenne pepper and salt in 4-cup (1 L) glass measuring cup until blended. Slowly whisk in melted butter. Microwave on Medium (50% power) until sauce thickens, 45 seconds to 1 minute. Whisk after 30 seconds and at end of cooking to produce a smooth sauce.
Step 3 Blender Method: Process egg yolks, lemon juice, cayenne pepper and salt in blender just until smooth. With blender running, slowly add melted butter, processing until thickened and fluffy.