I've made this 1000 times, easy!
1 stick butter, 3 yolks, lemon juice to taste.
Beat yolks. Melt butter and--whisking constantly--drizzle the butter into the eggs slowly in a thin stream, alternating with lemon juice. Salt/pepper to taste.
I skip the step of the last heating/beating, I think this is where people get messed up. Too hot and you get scrambled eggs...