Step 1

Brush a non-stick 10x15 jelly roll pan with oil and line with parchment paper. Brush the parchment paper lightly with oil as well. Preheat oven to 375°F.

Step 2

In a small heat-proof bowl, sift together cocoa powder and espresso powder. Pour hot water over them and mix with a spoon until completely smooth. Set aside.

Step 3

Sift together the sweet rice flour, oat flour, millet flour, baking powder, xanthan gum (if using), and salt in a small bowl. Set aside.

Step 4

Separate the eggs, placing the yolks in a large mixing bowl and the whites in a medium mixing bowl. Add cream of tartar to the egg whites and, using a hand mixer, whisk the egg whites, starting on low speed and increasing to high speed until soft peak form. When the beater is pulled out a peak should rise and the very tip should fall. Set aside.

Step 5

In the large mixing bowl, begin mixing the egg yolks on slow increasing to medium speed. Slowly pour in the sugar. Increase the speed and beat until pale yellow and forms ribbons. When a beater is lifted, the egg mixture should stay on the top for a few moments before reluctantly incorporating back into the mix.

Step 6

Add the vanilla extract, vegetable oil, and cocoa powder water mixture to the egg yolks and beat until just combined, scraping down the sides as needed.

Step 7

With a rubber spatula, fold in the flours until just incorporated, taking care not to overmix. Fold in 1/3 of the whipped egg whites to loosen the batter. Then carefully fold in the remaining whipped egg whites until just combined.

Step 8

Pour into prepared baking pan and use an offset spatula to evenly spread the batter over the pan. Bake for 15-16 minutes, until it gently springs back when pressed. Take care not to overbake or your cake will break when you try to roll it.

Step 9

When the cake comes out of the oven, let it cool for 2 minutes in the pan. Dust the top generously with cocoa powder. Place a wire rack over the top and flip the cake out of the pan. Remove the parchment paper and dust again with cocoa powder. Place a clean sheet of parchment paper and the back of a baking pan over the top and turn the baking pan upside down to flip the cake back right side up.

Step 10

Very carefully, roll the cake up using the parchment paper. If you roll too tight, your cake may break. If that happens, that's okay! Just remove the broken part (safe for mini trifles?) and roll again. Let cool on the wire rack, seam side down, for 45 minutes to an hour while you prepare the frosting.

Step 11

In a large mixing bowl with a hand mixer or the bowl of a stand mixer, beat the cream cheese until smooth, scraping the sides as needed. Slowly add the powdered sugar and vanilla, mixing until incorporated. Add 1/4 cup of the heavy cream at a time, mixing until smooth. Once all the heavy cream has been added, increase the speed to high and beat until stiff peaks form. Chill frosting while the cake roll cools. You can make the frosting up to a few days in advance and store it in the fridge until needed! It will stay soft enough to spread.

Step 12

When the cake roll is mostly cooled, very carefully and slowly unroll the cake. When you get to the middle, don't unroll it all the way. If the cake cracks a tiny bit while you're unrolling it, don't be too concerned, you can patch it up with frosting! Use an offset spatula to spread the frosting in a 1/2-inch layer starting in the middle and use the parchment paper to carefully reroll the cake. Keep the parchment paper rolled on the outside and chill for at least 2 hours before slicing and serving.

Step 13

When ready to serve, remove parchment paper and dust with powdered sugar. Slice into 1-inch thick slices and serve!