Step 1

Combine lemon zest and sugar in food processor.

Step 2

Pulse to mince zest, then process until zest is as fine as the sugar.

Step 3

Add egg yolks, lemon juice, process 10 seconds.

Step 4

With machine still running, pour in melted butter or margarine

Step 5

Transfer mixture to double boiler and cook over low heat until thickened, about ten minutes.

Step 6

Cool and refrigerate.