Preheat oven to 350℉. Spray a 10 x 15 jelly roll pan with nonstick spray. Line with parchment paper, and spray again with the nonstick spray.
Sprinkle a silicone mat (at least 10 x 15) or another sheet of parchment paper heavily with powdered sugar. Set aside.
In a stand mixer with balloon whisk attachment, beat the Egg Whites, Vanilla, and Cream of Tarter until frothy. Once combined and frothy, increase the speed to high. Mix until soft peaks form. Gradually add Sugar until it is all incorporated. Beat on high until stiff, glossy peaks form.
Remove bowl from mixer. Using a metal or wooden spoon, gently fold the Cake Flour in, 1/4 cup at a time, until all the flour is incorporated.
Spoon the batter into the prepared jelly roll pan and evenly spread it out.
Bake for 15-20 minutes, or until golden brown. Cool in pan for 5 minutes.
Once cooled for 5 minutes, quickly but carefully, invert the pan and release the cake onto the prepared silicone mat/parchment paper. Remove the baking parchment paper, setting it aside. Let cool for 5 minutes.
Loosely set the parchment paper that was used for cooking back on top of the cake and gently roll the cake, silicone mat, and parchment paper into a roll - starting at the short end. Set aside on a cooling rack to cool completely.