The Best Thick & Fudgy Oreo Cheesecake Brownies

0 Preheat your oven to 325°F and line a 9x9-inch pan with parchment paper, making sure it covers the bottom and sides so you can lift the brownies out easily later.
1 Start with the brownie mixture. Melt the butter in a large bowl and let it cool slightly so it is not too hot. Add the sugar and vanilla extract and mix until combined. Add the eggs one at a time, mixing well after each addition. The mixture should look thick and glossy.
2 Whisk in the flour, cocoa powder, and salt until evenly combined. Do not overmix.
3 Pour the brownie batter into the prepared pan and spread it evenly. Bake for 22-25 minutes to set the base, until the top looks matte and set (not shiny or wet).
4 While the brownie layer is baking, prepare the cheesecake mixture. In a bowl, mix the cream cheese and sugar until smooth and creamy with no lumps. Add the vanilla extract, egg, and sour cream, and mix until fully combined. Add the flour and mix just until incorporated.
5 Fold the chopped Oreo cookies into the cheesecake mixture until evenly distributed.
6 After the brownie layer has baked, remove it from the oven and gently pour the cheesecake mixture over the top, spreading it evenly.
7 Return the pan to the oven and bake for 33 to 38 minutes, until the cheesecake layer is set around the edges and slightly soft in the center.
8 Remove from the oven and let the brownies cool completely in the pan. For clean slices, refrigerate for at least 1 hour before cutting.