Preheat oven to 400 degrees. In a medium saucepan, mix together cornstarch, white sugar, salt, and nutmeg. Mix in sour cream. Add egg yolks, raisins, and lemon juice. Stir until thoroughly combined. Cook mixture over medium heat, stirring constantly until mixture thickens and boils. Boil and stir 1 minute. Pour mixture into baked pie crust. In a large glass or metal bowl, beat together egg whites and cream of tartar until foamy. Add brown sugar, 1 Tbsp. at a time, continuing to beat until egg whites are stiff and glossy. Beat in vanilla extract. Spread evenly over raisin filling, sealing meringue to crust edges. Bake in a 400-degree oven for 10 minutes until delicately browned.