Fresh sage and creamy Gorgonzola cheese add a richness and complexity of flavor to the mellow silkiness of fresh pumpkin. Roasting the pumpkin heightens its sweetness, which is balanced beautifully by the tangy cheese — but if you're in a hurry, the tart can also be made with good-quality canned pumpkin (see important note below). You can use your favorite savory (not sweet) pastry dough, or try our recipe.
Serve thin slices of the warm tart with a simple green salad and some crusty bread for a delicious and elegant luncheon or supper. The tart is best the day it is made, but it can be refrigerated, covered, for one day and then reheated in a 325-degree oven until hot.
Important note: Canned pumpkin can sometimes contain much more moisture than fresh, cooked pumpkin — but it's difficult to tell just by looking. To be safe, if you use canned instead of fresh pumpkin, empty the pumpkin into a fine mesh strainer lined with cheesecloth and let it rest for about 30 minutes. (You don't have to squeeze it.) This step will help equalize the moisture level and allow the filling to thicken as it should.
Roll out the pastry dough to fit a 9-inch fluted tart pan or a rectangular 4x13-inch tart pan with a removable bottom. After fitting the dough into the pan, run the rolling pin over the top of the pan to trim any excess dough hanging over the edge. Using a fork, prick the bottom of the pastry dough all over. Line the pan with a piece of parchment paper and fill with pie weights or dried beans. Refrigerate for at least 30 minutes.
Position a rack in the middle of the oven and preheat to 375 degrees F. Brush the cut surfaces of the pumpkin with some oil, season lightly with salt and pepper, and place it cut side up on a rimmed baking sheet. Bake until the flesh is very soft and has begun to brown slightly, 45 to 60 minutes. Let cool, covered with aluminum foil or an upside-down bowl.
Once the pumpkin is cool, scoop out the flesh and discard the skin. Place the pumpkin in a bowl and mash roughly with a potato masher. Reserve 1 cup of the pumpkin, then refrigerate or freeze the remainder for another use.
Place the chilled tart pan on a rimmed baking sheet and bake for 18 minutes. Remove the pie weights and paper and return the pastry to the oven to bake for an additional 5 minutes. Transfer the baking sheet to a wire rack and let the pastry cool.
Add half of the heavy cream and the nutmeg to the mashed pumpkin and stir to blend. Spread this mixture across the bottom of the pastry shell. Sprinkle the cheese on top.
Place the remaining cream, crème fraîche, eggs and egg yolk in a bowl and whisk to blend. Pour the custard into the tart pan. Arrange the sage leaves in a decorative pattern on top of the tart.
Bake the tart on the rimmed baking sheet until set in the middle and lightly golden, 30 to 35 minutes. Let the tart cool for at least 15 minutes before removing it from the pan and slicing with a serrated knife. Serve warm.