1/3cupDutch processed cocoa powder,plus more for dusting
1teaspooninstant espresso powder,optional
¼cupboiling water
2tablespoonsunsalted butter,softened
1teaspoonpure vanilla extract
6large eggs,separated
½cupgranulated sugar
¾teaspooncream of tartar
2tablespoonsplus 2 teaspoons granulated sugar
Instructions
Preheat the oven to 350 degrees Fahrenheit. Spray a 16-by-11-inch rectangular jelly-roll pan with nonstick cooking spray. Line with parchment paper, allowing the paper to extend over the sides by approximately ½ inch. Spray the parchment again with nonstick cooking spray. Place 1 tablespoon cocoa powder into the greased pan, rotating to coat all surfaces and knock out the excess. Set aside.
Using a whisk, blend cocoa powder, espresso if using, and boiling water until well blended and cocoa has dissolved.
Whisk in butter and vanilla and blend well. Set aside.
In the bow of an electric mixer, using the whip attachment, beat the 6 egg yolks and ½ cup granulated sugar on high speed until light and pale yellow, approximately 2-3 minutes.
On medium speed, add cocoa mixture to yolks and blend well. Pour mixture into a large mixing bowl.
Using a clean, dry, electric mixing bowl and clean, dry whip attachment, beat the 6 egg whites on high speed until foamy.
Add the cream of tartar and beat on high until soft peaks form.
Slowly add the 2 tablespoons and 2 teaspoons granulated sugar, beating on high speed until stiff peaks form. Scoop approximately 1/3 egg whites and whisk them into the cocoa and yolk mixture and whisk mixture to lighten the batter.
Add remaining whites on top of the cocoa mixture, and using a rubber spatula, fold together until only a few streaks remain. Do not over fold.
Pour batter into pan, spreading evenly, and bake for 18 minutes or until cake is slightly puffy and springs back when a finger is gently pressed into it. Sift approximately 1 tablespoon of cocoa over the surface of the cake. Place a clean, damp kitchen towel over the cake and allow it to cool.
Remove the towel and place a parchment-lined, 12-by-18-inch sheet pan over the cake and flip the cake over. Gently peel the parchment paper off the top of the cake.
Roll the cake roll with any desired filling using the bottom parchment paper as a guide to help you roll.
Notes
Makes 1 16-by-11-inch rectangular cake (which is also gluten-free!)