In a large bowl, stir together mascarpone cheese, confectioners sugar, pumpkin, ricotta and pumpkin pie spice until smooth. Stir in 1/4 cup nuts. Set aside.

In a chilled mixing bowl, beat cream with an electric mixer until stiff peaks form. Fold into pumpkin mixture. Cannoli can be made immediately or filling can be covered and chilled up to 4 hours.

To serve, spoon pumpkin mixture into a self-sealing plastic bag. Snip a 3/4 inch hole in one corner. Pipe filling into each cannoli shell so pumpkin filling extends to ends of shell. Sprinkle the ends with remaining nuts. Arrange on a serving platter and dust with confectioners sugar.