Sift dry ingredients together. Using a stand or hand mixer, blend together vanilla, egg yolks, pumpkin, oil and water. Make a hole in the dry ingredients and add pumpkin mixture, then beat all ingredients until smooth.
Beat egg whites until foamy, add cream of tartar, and beat until egg whites have stiff peaks. Fold into pumpkin batter.
Bake in a 10-inch un-oiled tube pan for 55 minutes at 325 degrees. Raise heat to 350 degrees and bake 15 minutes longer.
Remove from oven and invert pan to cool.
To remove, carefully run a table knife around the outside of the cake, then between the tube and the cake. Using a spatula, carefully release cake from the base of the pan. Slide onto a plate and then flip it to another plate.
Dust with powdered sugar. Serve with lightly sweetened whipped cream and fresh, seasonal fruit if desired.