1. Preheat oven to 350°F.
2. Fit one sleeve of dough into a 9-inch pie plate. Fold edges under, flute. Place pie plate in freezer until ready to use.
3. Combine the brown sugar, 1/2 cup cocoa, and flour in a large bowl. Combine mik and the next 5 ingredients, stir with a whisk until well-blended. Add milk mixture to brown sugar mixture; stir until combined.
4. Pour mixture into crust. Bake at 350°F for 40 minutes or just until set. Cool on a wire rack to room temperature. Cover and chill for at least 4 hours. (Resist the temptation to dig in before this!) Spread whipped topping evenly over filling; sprinkle with 1/2 teaspoons cocoa.