Pumpkin puree has long been a secret ingredient in all types of cakes and brownies and other baked goods where you want extra moistness, but not always is the flavor of the pumpkin so prominent as in this cake. Rather than use the canned variety, this recipe calls for cutting pumpkin into cubes and baking until tender, for a deeper pumpkin taste. Chopped toasted hazelnuts are also added, for a delicious result.