Spray a 9x13 cake pan with non-stick cooking spray. Line the pan with parchment paper strips, to help lift out the bars once they are set.
Add the biscoff cookies to a food processor. Pulse until the cookies resemble a rough crumb, and then start streaming the melted butter into the cookie crumbs while continuing to pulse until the cookies resembles wet sand.
25 Biscoff cookies, ½ cup Salted butter
Transfer the cookie mixture into the pan, and using your hand or the bottom of a dry measuring cup, press the crumb mixture into the bottom of the pan. Ensure that the mixture is tightly packed into the bottom, and transfer to the freezer.
Add the cold heavy whipping cream to a stand mixer bowl. Using the whisk attachment, whip the cream on a high setting until the cream has formed stiff peaks. Transfer the cream to a bowl, and set aside.
1 ½ cups Heavy whipping cream
To the same stand mixer bowl, add the softened cream cheese, sour cream and granulated and confectioner sugar. Using the paddle attachment, whip the cream cheese and sugar together until light and fluffy.
2 8 oz Cream cheese bricks, ½ cup Granulated sugar, ½ cup Confectioners sugar, 2 tablespoon Sour cream
Add the pumpkin puree, pumpkin spice, and vanilla to the mixture, and mix on medium speed until combined. Scrape down the sides of the bowl to ensure that there is no unmixed cream cheese at the side or on the bottom.
½ cup Pumpkin puree, 1 ½ teaspoon Pumpkin spice, 1 ½ teaspoon Vanilla extract
Add in the whipped cream in halves, and fold it in gently to incorporate the whipped cream into the cream cheese mixture. Take the rubber spatula under the mixture, and fold over. Do this with both halves of the whipped cream until the mixture is combined.
Transfer the mixture to the cake pan with the pressed cookie crust. Smooth the cheesecake mixture out with a rubber spatula, or an offset spatula if you would like an extra smooth top.
Refrigerate the cheesecake in the pan, for at least 8 hours. Cover the top of the cheesecake with cling wrap. When you are ready to serve, remove the cheesecake from the pan, and cut into 24 squares.
To serve, melt the chocolate and butter in the microwave in 15 second increments until smooth. Transfer the melted chocolate to a plastic sandwich bag, and cut off a small tip. Drizzle the chocolate over the cheesecake, and refrigerate the cheesecake bars for another 10 minutes.
½ cup Semi-sweet chocolate baking discs, 2 tablespoon Salted butter