Preheat the oven to 350°F and grease two 6-inch round cake pans. Line the bottoms with parchment paper.

In a medium bowl, whisk together the flour, sugar, and baking powder. In a separate bowl, beat the butter until smooth, then mix in the melted white chocolate, eggs, milk, and vanilla until combined.

Add the dry ingredients to the wet mixture and stir until just blended. Divide the batter evenly between the prepared pans.

Bake for 22 to 25 minutes, or until a toothpick inserted in the center comes out clean. Cool the cakes in the pans for 10 minutes, then turn them out onto a wire rack to cool completely.

To make the frosting, heat the heavy cream in a small saucepan until it just begins to steam. Remove from heat, add the remaining 6 ounces of white chocolate, and stir until smooth. Chill the mixture for 30 minutes, then whip until it thickens to a spreadable consistency.

Place one cooled cake layer on a plate and spread with a layer of frosting. Top with the second cake layer and cover the top and sides with the remaining frosting. Use a piping bag or spoon to add small ghost shapes on top, then press candy eyes into each ghost.