- Tart Shell: Preheat oven to 350 degrees F. Spray a 9 inch tart pan with cooking spray. Set aside.
- Cream butter and sugar together until light in color using an electric mixer or food processor. Add egg yolk and lemon zest mixing until well blended. Add flour and mix just until dough begins to form. Stop mixer, remove dough and shape into a disc. Cover with plastic wrap and refrigerate 25-30 minutes.
- Roll dough out into a circle on a floured work surface. Gently wrap dough around rolling pin and transfer to tart pan. Press dough evenly into tart pan. Bake in preheated oven 15-20 minutes or until golden brown. Remove from oven and cool 20 minutes before filling with caramel.
- Caramel Filling: Cook 1/4 cup sugar in a small sauce pan over medium heat until it begins to turn golden brown (caramelizes). Remove from heat. Slowly add LACTAID® Low Fat Milk. Return to low heat and stir until the sugar has melted into the milk, about 5-8 minutes. Set aside.
- Mix cornstarch and 1/2 cup sugar together. Add egg yolks. Mix until very well blended. While whisking, slowly pour half of the warm milk into the cornstarch mixture. Mix well using a wire whisk and then return to sauce pan. Cook caramel filling over medium low heat while stirring constantly until the mixture thickens, about 6-8 minutes.
- Pour caramel into pie crust. Chill in refrigerator 2-3 hours before serving.