Tarte au Fromage Potiron Alsacienne (Alsatian Pumpkin Cheesecake)

To make the Pumpkin Butter, add pumpkin puree, brown sugar, water and lemon juice in a deep medium-sized saucepan. Whisk ingredients together and cook under medium low heat for 30-40 minutes stirring occasionally to prevent mixture from sticking to the bottom of the pan and burning.

Pumpkin butter is ready when mixture has thickened up and has a deep brown-orange color. Allow to cool to room temperature before using.

To make the pastry crust, mix flour, salt, and butter with your fingers (or pulse in a food processor) until you get a crumbly consistency and pea-size bits of butter are still visible. Add the egg and water, mixing just until the dough comes together. Shape the dough into a disk, wrap in plastic wrap, and chill until firm - a minimum of 30 minutes.

Lightly butter a 9-inch (23-cm) springform pan. Take the dough out of the fridge, and roll to a 15-inch (38-cm) diameter circle. Transfer the dough into the springform pan, and ease it down to the base and up against the sides. Don’t worry if the dough pleats on itself or cracks. You can fold the edges of the dough over the rim of the pan to keep them upright and patch cracks with excess dough; this crust is meant to be rustic-looking. Put the pan in the fridge while you prepare the filling.

Preheat your oven to 350°F (180°C, or gas mark 4).

To make the filling, whisk together the Greek yogurt, heavy cream, sugar, flour, pumpkin butter, vanilla extract, pumpkin spice, cinnamon, and salt. Add in the egg yolks, and mix until just incorporated. In a separate bowl, beat the egg whites to a firm peak. Gently fold the egg whites into the Greek Yogurt-mixture with a spatula, until homogenous. The batter will be light and fluffy.

Take the pan out of the fridge and gently scrape the batter in, right to the edges of the crust. Bake for 40-45 minutes, until golden brown and a skewer comes out clean. The filling will have souffléd to about 1 inch (2.5 cm) above the top of the crust. Let the filling deflate to the same level as the crust in your oven, with the heat off, for about 15 minutes. Take the cheesecake out of the oven, and immediately flip it upside down onto a circular cooling rack (if you don't have a circular cooling rack, choose one with a pattern you like, as the top of the cheesecake will take on that pattern). Remove the pan, and let the cake cool completely to room temperature before flipping it back over.

Chill for 1 hour. Sprinkle with a thin layer of powdered sugar before serving.