Do not thaw.
Microwave: Remove cake from plastic film. Turn upside down on a microwave-safe plate. Loosen cake from cup by applying pressure to center of cup with thumbs while holding the edges. Do not remove cup. Microwave on HIGH for 40-50 seconds. Carefully remove cup. Let stand 3-5 minutes before serving.
Conventional Oven: Preheat oven to 400°F. Remove plastic film and place cake right side up, in its cup on a baking sheet. Heat for 15-18 minutes. Remove from oven. Let stand 3-5 minutes. Invert cake on serving plate and serve.