Preheat oven to 350°F. Grease and flour 10-inch tube or Bundt pan.
Combine hazelnuts and chocolate in food processor. Whirl until chopped medium-fine. Add brown sugar, cinnamon, allspice and 1 teaspoon of the vanilla. Whirl just until combined.
Combine flour, baking powder, baking soda and salt in bowl.
Beat together butter, sugar and remaining 2 teaspoons vanilla in large bowl at medium speed until smooth and creamy, 2 minutes. Beat in eggs, one at a time, until blended. On low speed, beat in sour cream. Beat in flour mixture just to combine. Spread one-third of the batter in bottom of prepared pan. Sprinkle with one-third of nut mixture. Repeat making 2 more layers, using up remaining ingredients.
Bake in 350°F oven for 45 to 55 minutes or until wooden pick inserted in center comes out clean. Transfer pan to wire rack to cool for 15 minutes. Run knife around edge. Remove from pan. Serve warm. Dust with confectioners sugar if you wish.