1. Heat oven to 350 degrees F. Coat three 8 x 2-inch round layer-cake pans with shortening; dust with flour, discarding excess.Cake:
2. Whisk flour, baking powder, pumpkin pie spice and salt in bowl.
3. Beat shortening in second bowl until smooth and creamy. Beat in sugar and maple syrup. Add eggs, one at a time, beating after each. Add maple flavor; beat until smooth. On low speed, beat in half of the flour mixture, then milk, then remaining flour mixture. Spread batter in prepared pans, dividing evenly.
4. Bake at 350 degrees F for 25 to 28 minutes, until golden brown. Cool in pans on rack 10 minutes. Remove cakes directly to rack to cool completely.Filling:
5. Beat cream cheese, butter and maple flavor in bowl until smooth. Add sugar; beat until good spreading consistency. Place cake layer on serving dish. Top with 1-1/4 cups filling. Place second cake layer on top, then remaining 1-1/4 cups filling. Top with third layer.Frosting:
6. In saucepan, heat cream just to a simmer. Pour over chocolate in a small bowl; whisk until smooth. Cool 5 minutes, until thicker but still pourable. Pour over cake, spreading to allow some to dribble down sides. Top with walnuts. Refrigerate 15 minutes before serving.