Mini Chocolate-Hazelnut Cheesecakes

Preheat the oven to 350 °. Line a 12-cup muffin tin with paper liners. Spray the liners with vegetable oil spray. In a food processor, combine the cookies, hazelnuts and butter and process to very fine crumbs. Divide the crumbs among the cups and, using a flat-bottomed glass, press on the crumbs to compact them. Bake for 5 minutes. Meanwhile, wipe out the food processor bowl. Add the cream cheese, Nutella, sour cream, eggs and sugar and puree until smooth. Spoon the filling into the cups until it nearly reaches the top; there may be a few tablespoons of leftover batter. Sprinkle the chocolate chips on top and bake for about 20 minutes, until the cheesecakes have risen and the surfaces are lightly cracked. Let the cheesecakes cool slightly, then transfer the muffin tin to a rack and freeze for 10 minutes, until the cheesecakes are slightly cooled. Serve chilled or at room temperature.