1. Prepare the crust: In a food processor, pulse the flour, sugar, salt, and cold butter until the mixture resembles coarse crumbs. You can also do this by hand with a pastry cutter or fingers. Gradually add ice water, one tablespoon at a time, until the dough just comes together. Form into a disk, wrap in plastic wrap, and refrigerate for at least 30 minutes—this helps prevent shrinking and makes rolling easier.
2. Pre-bake the crust: Preheat your oven to 375°F (190°C). Roll out the chilled dough on a lightly floured surface to about 1/8-inch thickness. Transfer it to a 9-inch tart pan, pressing into the edges and trimming any excess. Dock the bottom with a fork a few times to prevent bubbling. Line with parchment paper and fill with pie weights or dried beans. Bake for 15 minutes, then remove the weights and parchment, and bake another 8-10 minutes until lightly golden. Cool completely on a wire rack.
3. Make the chocolate ganache: Place chopped dark chocolate in a heatproof bowl. Heat the heavy cream until it just begins to simmer, then pour over the chocolate. Let sit for 2-3 minutes, then whisk until smooth. Pour the ganache into the cooled tart crust, spreading evenly. Chill for at least 30 minutes to set.
4. Prepare the pumpkin filling: In a mixing bowl, whisk together pumpkin, brown sugar, eggs, vanilla, and spices until smooth. Gradually add the heavy cream, whisking constantly to create a silky mixture.
5. Assemble the tart: Carefully pour the pumpkin filling over the chilled dark chocolate ganache layer. Smooth the top with a spatula.
6. Bake the tart: Bake in the preheated oven at 350°F (175°C) for 35-40 minutes, or until the filling is set but still slightly jiggly in the center. The edges should be firm, and a toothpick inserted in the center should come out clean.
7. Cool and serve: Allow the tart to cool completely on a wire rack. For best flavor, refrigerate for at least 2 hours before serving. Garnish with whipped cream or a dusting of cocoa powder if desired.

From my own experience, I’ve found that letting the tart chill overnight really helps develop the flavors. Plus, it makes slicing much cleaner—something I learned the hard way when I was in a rush and the slices fell apart!