1. To make the tart shell: In a large bowl, mix the flour, cornmeal, and salt. Using the coarse holes of a grater, shred the butter into the flour mixture and toss it with your fingers to coat. Cut until the mixture is full of coarse lumps. Quickly stir in the ice water just until the dough sticks together, then form the dough into a ball. Chill for 1 hour.

2. Preheat oven to 400°F. Roll out dough and fit into a 12-inch tart pan. Prick the shell all over and bake until edges are browned, about 10 minutes. Let cool on a cooling rack.

3. To make the filling: Sauté the squash and shallots in the olive oil in a large pan over medium-high heat, stirring. After 5 minutes, add the garlic and stir. Add the wine and salt and cover for 5 minutes, checking at the end to see if the pan is dry. When the squash is tender when pierced with a paring knife, uncover and cook until the liquids have evaporated. Remove from the heat and let cool.

4. Sprinkle some cheese in the shell and top with the squash mixture, the remaining cheese, and hazelnuts. Bake until the cheese is melted and golden on top, about 20 minutes. Slice in 6 wedges and serve warm.