Step 1: Prepare the cake layers

1. Preheat your oven to 350°F (175°C). Grease and flour two 9-inch (23 cm) round cake pans, or line them with parchment paper.
2. In a medium bowl, whisk together the flour, baking powder, and salt. Set aside.
3. In a large bowl, cream the butter, oil, and sugar until light and fluffy. Add the eggs one at a time, beating well after each addition. Stir in the vanilla extract.
4. Gradually mix in the dry ingredients, alternating with the milk, beginning and ending with the dry ingredients. Stir in the melted white chocolate until just combined.
5. Divide the batter evenly between the prepared pans and bake for 25-30 minutes, or until a toothpick inserted in the center comes out clean. Let the cakes cool in the pans for 10 minutes, then transfer to a wire rack to cool completely.

Step 2: Make the pineapple filling

1. In a medium saucepan, combine the drained crushed pineapple, sugar, cornstarch, and reserved pineapple juice.
2. Cook over medium heat, stirring constantly, until the mixture thickens and becomes glossy. Remove from heat and let cool completely.

Step 3: Make the white chocolate frosting

1. In a large bowl, beat the cream cheese and butter together until smooth and creamy.
2. Add the melted white chocolate and vanilla extract, mixing until fully incorporated.
3. Gradually add the powdered sugar, 1 cup at a time, and beat until smooth and fluffy.

Step 4: Assemble the cake

1. Place one cake layer on a serving plate or cake stand. Spread a layer of pineapple filling evenly over the top.
2. Place the second cake layer on top and spread the frosting over the top and sides of the cake.
3. Decorate with additional crushed pineapple or white chocolate shavings, if desired.

Step 5: Serve
Refrigerate the cake for at least 1 hour before serving for easier slicing.