Marbled Pumpkin Cheesecake with a Brownie Crust

Ingredient:

• 4 tablespoons unsalted butter, plus more for greasing the pan
• 2 ounces bittersweet chocolate, coarsely chopped
• 1/4 cup granulated sugar
• 1 large egg, lightly beaten
• 1/4 cup all-purpose flour
• 1/2 teaspoon baking powder
• 1/8 teaspoon kosher salt
• 1/4 cup finely chopped walnuts
• 4 ounces bittersweet chocolate, chopped
• 1 1/2 pounds cream cheese, softened
• 1 cup granulated sugar
• 4 large eggs, at room temperature
• 1 1/2 tablespoons cornstarch
• 1 teaspoon pure vanilla extract
• 2 cups canned pumpkin puree (16 ounces)
• 1/2 teaspoon cinnamon
• 1/2 teaspoon freshly grated nutmeg
• 1 pinch of ground cloves