Move the oven rack to the middle position and preheat the oven to 400°. Line an 8 x 8-inch square baking pan with aluminum foil, leaving an overhang on all sides, and spray the foil lightly with nonstick cooking spray.
Mix the brownie mix as per the box instructions.
Pour batter into prepared pan and bake the brownies according to box directions. Once the brownies are done baking, move them to a wire rack while preparing the cheesecake layer. Keep the oven on.
MAKE THE CHEESECAKE LAYER:
In the bowl of a stand mixer fitted with a paddle attachment, or in a medium bowl with a hand mixer, beat together the cream cheese, powdered sugar, egg, and vanilla extract until smooth and combined.
Pour the cheesecake batter on top of the baked brownies, and then bake for 26-28 minutes, or until the cheesecake layer is golden on top and set. Move the brownies to a wire rack to cool until just warm.
Press the cut-up Snickers into the cheesecake layer. Then, cover the brownies with foil and chill in the refrigerator for at least 2 hours.
Use the foil overhang to remove the cheesecake brownies from the pan. Peel the foil down from the brownies' sides and cut the brownies into 9-12 squares. Serve.
If you're feeling super decadent, then you can drizzle some chocolate sauce or salted caramel over the brownies right before you serve them.
You can slice the cheesecake brownies into 9-12 pieces easily.