Mix yolks and juice in saucepan WITHOUT heat. Turn on LOW heat. Whisk
gently until it's mayonaiss-ey. Add cayenne, salt and pepper. Whisk
in butter one slice at a time until it looks like it can't hold
anymore.
If it starts to curdle, add an ice cube and whisk around until it
settles.
Adjust the lemon juice to taste: 1/4 lemon for less intense, 1/2 for
more intense.