Preheat the oven to 350℉.
Line the baking pan with parchment. Grease with an oil spray or butter. Then combine the tablespoon of cocoa powder and the tablespoon of powdered sugar. Shake with half of mixture, reserving the remaining for sprinkling on the clean dish towel later.
In a stand mixer or a bowl using a hand mixer, beat the egg yolks with ¼ cup sugar, until thick and lemon colored.
Beat in the cocoa powder and the brown rice flour, the vanilla, and the pinch of salt.
Pour into a bowl. Use the whisk attachment and a clean dry bowl to whip the egg whites. Start the mixer speed on medium low. When bubbles appear, increase the speed and gradually add in the remaining tablespoon of sugar. Beat until peaks form. Fold into the chocolate mixture in thirds.
Spread into the prepared parchment lined pan. Smooth. Bake for 13-16 minutes or until a toothpick comes out clean when poked in the center. Remove to a wire rack to cool for 10 minutes. Shake a clean dish towel with the remaining cocoa powder and powdered sugar mixture. Invert the cake onto the dish towel. Let cool 15 minutes. Roll up gently with the towel. Set on the wire rack to finish cooling.
Whip the cream in a clean bowl until lines begin to appear from the beater. Add the sugar and vanilla and whip until pillowy and fluffy. Stir once and refrigerate until ready to fill the cake.