Heat oven to 350. Grease and flour 2 round 9x1-1/2 inch pans.
Reserve 1 cup pumpkin, set aside.
Beat remaining pumpkin and all remaining ingrediants except powdered sugar, whipping cream, 1/2 teaspoons vanilla, and 1/4 teaspoons pumpkin pie spice in a large bowl with an electric mixer on low speed 30 seconds scraping bowl constantly.
Beat on medium speed 4 minutes, scraping bowl occasionally. Divide batter evenly between pans.
Bake 25-30 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes, remove from pan, cool completely, about 1 hour.
Beat the powdered sugar, whipping cream, vanilla, and pumpkin pie spice in chilled large bowl on high speed until stiff. Gently fold in pumpkin.
Place 1 cake layer, rounded side down on serving platter; spread with half of pumpkin cream. Top with second layer, rounded side up. Spread remaining cream on top, top with very finely chopped hazelnuts if you wish.