Preheat the oven to 350°F. Grease a 9-inch springform pan.
In a medium saucepan, melt 1/2 cup of butter over low heat. Remove from heat and stir in granulated sugar and brown sugar until well combined.
Add eggs one at a time, mixing well after each addition. Stir in 1 teaspoon of vanilla extract.
In a separate bowl, whisk together flour, cocoa powder, and salt. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.
Pour the brownie batter into the prepared springform pan and spread evenly.
Bake for 20-25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs. Remove from the oven and let cool completely in the pan.
In a large mixing bowl, beat the softened cream cheese, peanut butter, powdered sugar, and 1 teaspoon of vanilla extract until smooth and creamy.
In another bowl, whip the heavy cream until stiff peaks form. Gently fold the whipped cream into the peanut butter mixture until fully combined.
Spread the peanut butter cheesecake mixture over the cooled brownie layer in the springform pan. Smooth the top with a spatula.
Refrigerate for at least 4 hours, or overnight, to set.
To serve, carefully remove the sides of the springform pan. Slice and enjoy!