To prepare a warm apple buttermilk custard pie recipe, you will first need to prepare your pie crust. Preheat the oven to 375?F (190?C) and grease the pie shell with butter or margarine. Place the sugar, butter, cinnamon, and vanilla extract in the bowl of an electric mixer and beat on medium speed until the mixture is light and fluffy, about 5 minutes. Add the egg yolks and mix until they are fully incorporated. Pour the apple mixture into the crust shell and stir to combine. Bake for 35 to 40 minutes or until crust is golden brown. Serve warm with whipped cream or ice cream.