Preheat oven to 350 degrees. Preheat an ungreased baking sheet in the oven.
With electric mixer, mix sugar and cocoa, then gradually add eggs, milk, butter, vanilla, and preserves until well-blended. Whip until thickened.
Pour into prepared crust (use either store-bought or make your own). Put pie onto preheated baking sheet and back 55-60 minutes or until the center is puffy. Coll completely before serving, and garnish with whipped topping if desired.