Preheat oven to 375°. Line a 15 x 10-inch jelly roll pan with foil, leaving an extra 1-inch over-hang so that you can easily lift the cake out after baking. Spray with cooking spray (I like the ones with flour in them) to prevent sticking.
In a medium bowl, mix together the flour, baking powder, baking soda, pumpkin pie spice and salt until combined.
In the bowl of a stand mixer, whisk eggs and granulated sugar for 1 minute until thick. Add the vanilla and pumpkin, and whisk until just combined. With the mixer on low speed, add the flour mixture and mix until just combined.
Spread the batter evenly into prepared pan. Bake for 13 to 15 minutes, or until top of cake springs back when touched. Carefully lift the cake out onto a flat surface. While the cake is baking, set a large, clean kitchen towel out on a large work surface. Sprinkle liberally with powdered sugar (about 1/4 cup). As soon as the cake comes out of the oven, turn it over on the kitchen towel sprinkled with powdered sugar. Remove foil carefully. Working from the short end, fold the edge of the towel over the cake. Roll tightly, rolling up the cake into the towel. Let cool completely while rolled, at least one hour.
While the cake is cooling, make the maple buttercream (instructions below.)
When cake is cool, carefully unroll the towel. Spread the maple buttercream over the cake, as evenly as you can. Roll the cake again, gently but tightly (and withouth the towel this time.) Wrap in plastic wrap to prevent drying out, and refrigerate for at least one hour, up to overnight.
When ready to serve, sprinkle powdered sugar on top, slice the cake and serve with pumpkin pie sauce, if you like!