Prepare the Cake BatterPreheat your oven to 350°F (175°C). Grease and flour two or three 6-8 inch round cake pans.
In a mixing bowl, combine all-purpose flour, baking powder, baking soda, and salt. Set aside.
Cream butter and sugar together until light and fluffy. Add the eggs, one at a time, beating well after each addition.
Stir in the vanilla extract.
Gradually add the dry ingredients to the wet mixture, alternating with milk, starting and ending with dry ingredients. Mix until just combined.
Bake the Cake ; Divide the batter evenly between the prepared pans. Smooth the tops with a spatula.
Bake for 30 minutes, or until a toothpick inserted into the center comes out clean.
Allow the cakes to cool in the pans for 10 minutes, then transfer to a cooling rack to cool completely.
Prepare the Piñata Shell (Optional)Melt the chocolate chips in a microwave or double boiler until smooth.
Use a dome mold to create the piñata shell by spreading the melted chocolate evenly over the mold. Let it set in the fridge for 20-30 minutes, then gently remove the shell.
Assemble the Cake ; Trim the tops of the cake layers to ensure they are flat using a sharp knife or cake leveler.
Place the first cake layer on a cake board or serving plate. Spread a layer of frosting over it.
Place the second cake layer on top and repeat if you have a third layer.
Using a round cutter or a knife, carve a hole in the center of the cake layers (excluding the topmost layer).
Add the Candy Filling Fill the hollow center of the cake with, candy or sprinkles of your choice.Place the top layer over the filled cake to seal it.
Frost the Cake Apply a thin crumb coat of frosting over the entire cake to seal in crumbs. Chill for 15 minutes.
Spread a final layer of frosting evenly across the cake, using a spatula for a smooth finish.
Decorate and Add the Shell Decorate the cake with additional frosting, sprinkles, or edible decorations as desired.
Carefully place the chocolate dome on top of the cake to cover it completely.
Serve and Smash!Present the cake with a small hammer or wooden mallet for smashing.
Let the guest of honor smash the dome to reveal the surprise treats inside!