**Prepare the Cake:** Bake the yellow cake in a 9x13-inch baking dish according to the package instructions. Let the cake cool completely.
**Make the Cream Filling:** In a mixing bowl, beat the softened butter and powdered sugar until light and fluffy. Add the marshmallow creme and vanilla extract, mixing until smooth and creamy.
**Layer the Cake:** Once the cake is cooled, use a sharp knife to slice it in half horizontally, creating two layers. Carefully lift off the top layer and set it aside.
**Add the Filling:** Spread the cream filling evenly over the bottom layer of the cake. Gently place the top layer of the cake back on.
**Add the Topping:** Spread the whipped topping evenly over the top of the cake.
**Decorate:** Sprinkle with sprinkles or crushed Twinkies for a decorative touch.
**Chill:** Refrigerate the cake for at least 1 hour before serving to let the layers set.