Preheat your oven to the temperature specified on the brownie mix package. Grease a baking pan (a square pan works nicely).
Prepare the brownie batter according to the brownie mix instructions.
While the brownie batter is prepared, roast your sweet potato. Prick the skin with a fork a few times, then bake it at 400°F (200°C) for 45 minutes to an hour, or until tender. Once cooked, let it cool slightly, then scoop out the flesh and mash it until smooth.
In a separate bowl, cream the softened cream cheese and sugar until light and fluffy. Beat the mashed sweet potato, egg, and vanilla extract until well combined.
Pour the brownie batter into the prepared pan. Spread the cheesecake layer evenly over the brownie batter.
Bake for 50-60 minutes, or until a toothpick inserted near the center comes out almost clean. The cheesecake layer might still wobble slightly, but that’s okay.
Take the brownies out of the oven and let them cool in the pan for 15 minutes. Sprinkle with chocolate chips (optional) and let them cool completely before cutting and serving.