Preheat oven to 350°F. Butter 15x10x1-inch baking pan. Line pan with wax paper; butter paper. Mix granulated sugar, flour, baking powder, 2 teaspoons of the pumpkin pie spice and salt in large bowl. Stir in eggs and pumpkin until well blended and smooth. Spread evenly in prepared pan.
Bake 15 to 20 minutes or until toothpick inserted in center comes out clean. Place clean kitchen towel on work surface; dust with 2 tablespoons confectioners' sugar. Loosen cake around sides of pan with small knife. Turn out onto sugared towel, wax paper-side up. Fold 1 side of towel over short side of cake, then roll up cake jelly-roll style. Cool cake completely.
Mix cream cheese, 1 cup confectioners' sugar, butter, vanilla and remaining 3/4 teaspoon pumpkin pie spice in medium bowl until well blended and smooth. Stir in walnuts, if desired. Unroll cake onto towel. Peel off wax paper. Spread cream cheese mixture evenly over cake. Using towel, roll up cake and place seam-side down on serving platter. Trim ends of cake.
Refrigerate 1 hour or until ready to serve. Sprinkle cake with additional confectioners' sugar just before serving.