Preheat the oven to 350°F (175°C). Grease and line a 9x9-inch baking pan with parchment paper.

In a medium saucepan, melt butter and chopped chocolate over medium heat, stirring occasionally until smooth. Remove from heat and let cool for 5 minutes.

In a large mixing bowl, whisk together granulated sugar, brown sugar, eggs, and vanilla extract until glossy. Stir in the melted chocolate mixture.

Sift the flour, salt, and baking powder into the bowl and mix until just combined. Pour the brownie batter into the prepared baking pan and spread into an even layer.

In a medium bowl, beat the softened cream cheese until smooth and creamy. Add granulated sugar, vanilla extract, and egg, beating until fully combined. Stir in the sour cream until smooth.

Gently spoon the cheesecake mixture over the brownie base, spreading evenly with a spatula.

Gently press chopped Milky Way pieces into the cheesecake layer, distributing them evenly.

Drizzle caramel sauce over the top and swirl gently with a knife or toothpick using figure-eight motions to create a marbled effect.

Bake for 35-40 minutes, until the brownie layer is set and a toothpick inserted comes out with moist crumbs. The cheesecake layer should have a slight jiggle in the middle.

Let the brownies cool in the pan for 15-20 minutes, then transfer to the refrigerator to cool completely for at least 1 hour before slicing.

Slice into 16 squares using a hot, dry knife (run under hot water and wipe clean between cuts). Serve cold or at room temperature, optionally drizzled with extra caramel sauce.