Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking dish. In a mixing bowl, whisk together 1 cup of all-purpose flour, ½ cup cocoa powder, ½ teaspoon baking soda, and a pinch of salt.

In another bowl, cream together ½ cup unsalted butter and 1 cup light brown sugar until smooth. Add 1 egg and 1 teaspoon vanilla extract, mixing until fully combined.

Gradually incorporate the dry ingredients, then fold in 1 cup semi-sweet chocolate chips.

Spread the Double Chocolate layer batter evenly in the prepared baking dish. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.

Once done, remove from the oven and let it cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely before adding the next layer.

While the Double Chocolate layer cools, repeat a similar process to create the Classic Chocolate Chip layer using the same ingredients and measurements as the Double Chocolate layer.

Pour the Classic Chocolate Chip batter over the cooled Double Chocolate layer in the same baking dish. Bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean.

Let this layer cool in the pan for about 10 minutes, then carefully transfer it to the wire rack to cool completely.

Next, cream ½ cup of softened unsalted butter with ½ cup light brown sugar and ½ cup granulated sugar until creamy for the Funfetti layer.

Add in 1 large egg and 1 teaspoon vanilla extract, mixing until combined. Gradually blend in a package of Funfetti cake mix along with ½ cup of all-purpose flour, and finally, fold in a handful of colorful sprinkles and ½ cup of white chocolate chips.

Layer the Funfetti batter over the cooled Classic Chocolate Chip layer, spreading it out evenly.

Bake for 20-25 minutes, or until a toothpick comes out clean from the center. After baking, allow the Funfetti layer to cool in the pan for 10 minutes before transferring it to a wire rack to cool completely.

While the final layer cools, make the vanilla buttercream by beating ½ cup of unsalted butter until smooth. Gradually add in 3 cups of powdered sugar and mix on low speed.

Once incorporated, pour in 1 teaspoon vanilla extract and add a tablespoon of water or cream as needed to achieve your desired frosting consistency. Beat until fluffy and creamy.

Once all three layers are cool, place the Double Chocolate layer on a serving platter, then top it with a generous spread of vanilla buttercream. Next, place the Classic Chocolate Chip layer on top and frost that layer as well. Finally, add the Funfetti layer on top and finish with the remaining vanilla buttercream.