Beat butter and sugar in electric mixer until blended. Add eggs and egg yolks, 1 at a time, beating just until blended after each addition.

Gradually add lemon juice to butter mixture and beat until blended.

Stir in zest.

Transfer mixture to a heavy 4-quart saucepan and cook, whisking constantly over medium heat until mixture thickens and easily coats the back of a spoon, about 14-16 minutes.

Transfer curd to a bowl, place plastic wrap directly on to of warm curd to prevent a film from forming.

Chill until firm, about 4 hours. refrigerate in an airtight container up to 2 weeks.