8 tablespoons (4 ounces) (1 stick) unsalted butter,
6 ounces good quality dark chocolate, chopped
2 cups plain flour
1 teaspoon baking powder
1/8 teaspoon cayenne pepper
1/2 teaspoon salt
1 1/2 sugar
4 large organic eggs
1 tablespoon pure vanilla extract
1 1/4 cups pumpkin
1/4 cup vegetable oil
1 1/2 teaspoon ground cinnamon
1/4 teaspoon ground nutmeg
1/4 all spice
1/2 cup chopped hazelnuts
Preheat oven to 350 degrees.
Generously grease a 9-inch square baking dish with butter. Melt the dark chocolate and butter by gently heating in a heavy based pan.
Sieve together flour, baking powder, cayenne, and salt in a large bowl; set aside. Beat together the sugar, eggs, and vanilla until fluffy and pale about five minutes. Fold in the flour.
Pour half of batter into a separate bowl and stir chocolate mixture into it. In other bowl, stir in the pumpkin, oil, cinnamon, and nutmeg. Transfer half of chocolate batter to prepared pan and top with half the pumpkin layer. Repeat the layers.
With a small wooden spoon gently swirl the two batters together to create a marbled effect. Sprinkle with hazelnuts. Bake until set, for about forty minutes. Let cool in pan on a wire rack.