crust

4 tablespoons unsalted butter
2 ounces bittersweet chocolate, coarsely chopped
1/4 cup sugar
1 large egg, lightly beaten
1/4 cup all-purpose flour
1/2 teaspoon baking powder
1/8 teaspoon salt
1/4 cup finely chopped walnuts

cheesecake

4 ounces bittersweet chocolate, chopped
1 1/2 pounds cream cheese, softened
1 cup sugar
4 large eggs, at room temperature
1 1/2 tablespoons cornstarch
1 teaspoon pure vanilla extract
2 cups canned pumpkin puree (1 pound)
1/2 teaspoon cinnamon
1/2 teaspoon freshly grated nutmeg
Pinch of ground cloves