Preheat the oven to 350F. Line a jelly roll pan (10”x15”x1”) with parchment paper and spray the pan and parchment paper very well with nonstick cooking spray.
In the bowl of a stand mixer fitted with the whisk attachment, beat the egg whites and cream of tartar on medium-high speed until stiff peaks form.
In a separate bowl, whisk together the egg yolks, granulated sugar, and vanilla until combined. Add the vegetable oil and whisk to combine.
In a separate bowl, whisk together the gluten free flour, cocoa powder, cornstarch, baking powder, salt, and espresso powder.
Add the dry ingredients to the egg yolk mixture and stir just until no dry streaks remain.
Add half of the egg whites to the batter and very gently fold them in – you don’t want to deflate the air in the egg whites so make sure to fold slowly and gently, just until fully combined. Add the remaining egg whites and continue to fold them gently into the batter.
Spread the batter into the prepared pan and bake for 10-12 minutes, or until the top springs back when touched and a cake tester just barely comes out clean. Make sure not to over-bake!
While the cake is in the oven, lay a lint-free towel on your counter and dust it generously with powdered sugar.
Allow the cake to cool in the pan for 2 minutes, and then very carefully turn it out onto the prepared towel. Fast and fearless is the best way–one quick flip!
Dust the top of the cake with powdered sugar and carefully use the towel to roll the cake into a log. Set the cake aside and cool completely at room temperature (at least 2 hours).