Prepare the Crust: Line an 8-inch square pan with parchment paper, ensuring an overhang on two sides for easy lifting. In a food processor, pulse the Biscoff cookies until they form fine crumbs. Pour in the melted butter and pulse again until the crumbs are well moistened. Press this buttery mixture firmly and evenly into the bottom of your prepared pan. Place the pan in the freezer for at least 30 minutes to chill while you get the filling ready.
Whip the Creamy Filling: In a large mixing bowl, combine the room-temperature cream cheese, ricotta cheese, and powdered sugar. Using an electric mixer, beat these ingredients together until the mixture is beautifully smooth and completely combined, ensuring there are no lumps.
Add Flavor and Mix-ins: Stir in the vanilla extract, and if you choose, the optional cinnamon and lemon zest for an added layer of delightful flavor. Gently fold in the mini chocolate chips and chopped pistachios with a spatula until they are just evenly distributed throughout the creamy filling.
Assemble and Chill: Carefully spread the rich, creamy filling over your chilled cookie crust, smoothing the top with an offset spatula. Cover the pan tightly with plastic wrap and refrigerate for a minimum of 4 hours, or ideally overnight, to allow the bars to set perfectly firm. This passive chilling time is essential for easy slicing!
Slice and Enjoy: Once thoroughly chilled, use the parchment paper overhang to gently lift the entire slab of bars out of the pan and onto a cutting board. For neat, clean slices, use a long, sharp knife, running it under hot water and wiping it dry between each cut. Garnish with extra mini chocolate chips or chopped pistachios if desired.