Preheat your oven according to the brownie mix instructions. Grease your 9x13-inch baking pan. Prepare the brownie mix as directed on the box, reserving about six Oreos for later use. Pour it into your greased pan and spread it evenly.
Place your brownie base in the oven and bake according to package instructions until set but still soft in the middle, usually around 20 minutes.
In a mixing bowl, combine softened cream cheese, granulated sugar, egg, vanilla extract, and sour cream. Beat until smooth and creamy.
Once your brownie base is baked and slightly cooled, pour the cheesecake filling over it evenly. Crumble the reserved Oreos over the top and gently press them down.
Return your pan to the oven and bake for an additional 30–35 minutes until set, with a slight jiggle in the center.
Heat heavy whipping cream until just simmering, then pour it over chocolate chips in a bowl. Let it sit for about five minutes before stirring until smooth.
Spread your ganache over cooled bars evenly. Chill in the refrigerator for at least two hours before cutting into squares.