In a metal bowl or in the top of a double boiler, combine all eggs, egg yolks, sugar, lemon zest, and lemon juice.
Place bowl over pan with a few inches of water. Do not let bottom of pan touch water.
Turn heat to high, add butter slices and begin stirring with a whisk. Continue stirring to avoid burning.
Cook until mixture becomes thick and coats the back of a spoon.
Remove from heat. Pour mixture into a very fine sieve. Use a spatula to push mixture through sieve.
Let cool a few minutes. Cover with plastic wrap making certain plastic wrap is directly touching the lemon curd. This helps avoid a skin forming on the surface.
Cool in refrigerator for a least 2 hours.