1. Preheat your oven to 350F (175C). Grease and flour three 8-inch round cake pans.

2. In a bowl, whisk together the flour, baking powder, and salt. Set this mixture aside.

3. In a large mixing bowl, beat the room temperature butter and granulated sugar together until light and fluffy.

4. Gradually add egg whites and mix well. Pour in the melted white chocolate and vanilla extract, blending until smooth.

5. Alternately add the flour mixture and the whole milk to the butter mixture, starting and ending with the flour mixture. Mix until just combined.

6. Divide the batter evenly among the prepared cake pans. Bake for 25-30 minutes or until a toothpick inserted into the center comes out clean. Let the cakes cool in the pans for 10 minutes before turning them out onto a wire rack to cool completely.

7. For the pineapple filling, combine chopped pineapple, granulated sugar, cornstarch, lemon zest, and lemon juice in a saucepan over medium heat. Cook, stirring, until the mixture thickens. Allow to cool completely.

8. For the vanilla buttercream frosting, beat the room temperature butter until creamy. Gradually add the sifted powdered sugar and melted white chocolate, mixing well until smooth. Stir in the vanilla extract and heavy cream until the frosting reaches your desired consistency.

9. To assemble the cake, place one layer on a serving plate. Spread a generous amount of pineapple filling over the top. Add the second layer, repeating the filling process, then finish with the third layer.

10. Frost the entire cake with the vanilla buttercream, smoothing it out as desired. Decorate with white chocolate shavings or pieces of pineapple if you want that extra touch.

**Nutritional Information:**

This cake is rich and indulgent, with a serving containing approximately 450 calories, 6g protein, and 24g fat. Make sure to enjoy it in moderation for a delightful treat!

**Time:**

Preparation time: 30 minutes | Cooking time: 30 minutes