Preheat the oven to 375 F.For the graham cracker crust: Combine the graham cracker crumbs with the sugar and melted butter. Stir to combine. Press the crust mixture into a 9-inch pie pan, pressing along the bottom and up the sides. Bake the crust for 7-8 minutes. Remove from the oven and set aside.Reduce the oven temperature to 350 F.
For the pie filling: Whisk the egg yolks. Add the remaining ingredients except for the citric acid and whisk until thoroughly combined and no lumps of sour cream are remaining. Whisk in the citric acid. Pour the filling into the pie shell. Bake for 20-25 minutes or until set but still slightly jiggly. Remove from the oven and allow to cool before transferring the pie to the refrigerator to chill for at least one hour before serving. Decorate with whipped cream or as desired. Slice and serve.