Preheat oven to 350°F. Spray a square springform pan with baking spray or line a 9×9 baking pan with parchment paper and then spray with baking spray. Set aside.
Melt the butter and chocolate in a small saucepan over medium low heat, constantly stirring until completely melted. Remove from the heat and whisk in the cocoa powder, sugar, eggs and vanilla. Add the flour and baking powder; carefully combine. Transfer to the prepared pan and set aside.
Place the white chocolate and the shortening in a heatproof bowl set over a pan of simmering water (make sure the base of the pan is not touching the water), stirring often. Once the chocolate has melted, remove the bowl from the pan of hot water and set aside for 5 minutes to slightly cool.
In an electric mixer with a paddle attachment, beat the cream cheese on medium-high speed until smooth. Lower the speed to medium-low and gradually add the eggs, followed by the sour cream, vanilla extract, and the melted white chocolate. Beat until combined. For a pink cheesecake batter add in the crushed peppermint candies.
Pour mixture over the brownie batter. Smooth over the top and place pan on a baking sheet. Bake for 35 minutes (convection bake) or 40 minutes (regular bake). Once baked, remove from oven and let cool for at least 2 hours. (Refrigerate to speed this process up if needed).
Melt the butter and chocolate in a small saucepan over medium low heat, constantly stirring until completely melted. Let the mixture cool for 2-3 minutes, then pour and spread evenly over the top of the chilled cheesecake.