Whisk your egg yolks, heavy cream together into a bowl & set aside. Into a large sauce pan add half and half, lemon zest and sugar. Heat over medium heat stirring frequently until sugar dissolves. Remove from heat. Add some of the warm half and half mixture to the egg yolk mixture into order to temper. GRADUALLY add the egg yolk mixture into the half and half mixture and stir well to combine. Return to medium heat and cook until mixture thickens. Remove from heat stir in vanilla extract.
Allow pan to cool slightly cover with saran wrap and place into the fridge to cool completely. When you’re ready to make your gelato stir in the lemon juice and follow instructions on your gelato maker!