CAKE: Preheat oven to 350°F Butter 15x10-inch baking pan. Line pan with wax paper; butter paper.
In a large bowl, mix (I used a wisk) the sugar, flour, baking powder, 2 teaspoons of the pumpkin pie spice and salt. Stir in eggs and pumpkin until well blended and smooth. Spread evenly in prepared pan. Bake 15-20 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 (I did it in the fridge).
FILLING: In a medium bowl, mix cream cheese, 1 cup confectioners' sugar, butter, vanilla and pumpkin pie spice until well blended and smooth. Stir in walnuts, if desired.
ASSEMBLY: 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.
Enjoy right away or refrigerate until ready to serve. Sprinkle cake with additional confectioners' sugar just before serving.