In a large mixing bowl, combine granulated sugar and eggs, whisking together for about 2 minutes until well blended. Slowly incorporate melted butter and vanilla extract, stirring until fully combined. Gradually add in the cocoa powder and flour, mixing just until the dry ingredients disappear. Pour the brownie batter into a greased 9x13-inch baking pan and bake at 350°F (175°C) for 25-30 minutes.

Once baked, remove the brownies from the oven and let them cool in the pan for about 1 hour at room temperature. After they’ve cooled, transfer the pan to the refrigerator and chill for an additional hour.

In a mixing bowl, beat the cream cheese until smooth and creamy. Gradually add the powdered sugar and peanut butter, mixing until the mixture is uniform and fluffy. In a separate bowl, whip the heavy cream until stiff peaks form. Gently fold the whipped cream into the peanut butter cream cheese mixture until fully combined. Spread this cheesecake layer evenly over the cooled brownie base.

In a small saucepan, melt the chocolate chips along with a splash of heavy cream over low heat, stirring until smooth and glossy. Once melted, remove from the heat and carefully spread the ganache over the cheesecake layer.

Refrigerate the assembled bars for at least 6 hours to set perfectly.

When ready to serve, remove the bars from the refrigerator and slice them into squares. Garnish with crushed Reese's cups on top.