In large pan, beat egg yolks and add rest of ingredients except butter. Cook under medium heat to a slow boil, stirring constantly. Remove from heat and add butter and stir until dissolved. Cool for five (5) minutes. Pour into cooled crust.
Cool on kitchen table for about 1 hour - cover with wax paper and refrigerate overnight. Whipped cream can be used with 1/2 teaspoon almond or vanilla flavoring.