6 tablespoons unsalted butter, plus more for the pan
2 ounces semisweet chocolate, chopped
1/3 cup sugar
2 large eggs
2/3 cup all-purpose flour
2 tablespoons unsweetened cocoa powder
1/4 teaspoon baking powder
Pinch of salt
8 ounces milk chocolate, chopped
1 cup heavy cream
3 8-ounce packages cream cheese, at room temperature
1 cup sugar
3 large eggs
1 tablespoon pure vanilla extract
2 ounces white chocolate, for topping