1. Gather Your Equipment: Prepare three 9-inch round cake pans, mixing bowls, a hand or stand mixer, and a spatula.
2. Preheat the Oven: Set the oven temperature to 350°F (175°C) to ensure even baking.
3. Mix Dry Ingredients: In a large bowl, whisk together all-purpose flour, baking powder, and salt until fully combined.
4. Cream Butter and Sugar: Beat softened unsalted butter with granulated sugar in a separate bowl until light and fluffy (about 3-5 minutes using a mixer).
5. Add Eggs and Vanilla: Incorporate eggs, one at a time, into the butter mixture, followed by the vanilla extract, ensuring a smooth blend.
6. Combine Wet and Dry Ingredients: Gradually alternate adding the flour mixture and whole milk to the butter mixture, beginning and ending with the flour. Mix until the batter is smooth.
7. Divide the Batter: Evenly separate the batter into three bowls.
8. Prepare the Chocolate Layer: Mix cocoa powder into one bowl of batter until well incorporated.
9. Prepare the Strawberry Layer: Add strawberry puree to another portion of the batter and stir until fully combined.
10. Prepare the Vanilla Layer: Leave the final portion plain to retain the vanilla flavor.
11. Prepare Cake Pans: Grease cake pans with butter or cooking spray, line them with parchment paper, and divide the three batter portions equally across the pans.
12. Bake the Cake Layers: Place the pans in the preheated oven and bake for 25-30 minutes, checking doneness with a toothpick inserted into the center—it should come out clean.
13. Cool the Layers: Let the cakes cool in the pans for 10 minutes, then transfer them to wire racks to cool completely.
14. Assemble the Cake: Begin layering with the vanilla layer at the bottom, followed by the strawberry and chocolate layers. Spread a thin layer of frosting between each layer.
15. Frost the Cake: Apply frosting evenly across the entire cake, including the sides, using an offset spatula for a smooth finish.
16. Decorate as Desired: Add final decorations like strawberries, cocoa powder, or sprinkles for a polished look.
17. Serve the Cake: Slice and enjoy your colorful and flavorful Neapolitan cake.
18. Store Leftovers: Wrap remaining cake tightly with plastic wrap or store in an airtight container. Keep it in the refrigerator for up to five days or freeze for longer storage.