Preheat oven to 350°F. Line a 17×12 inch jelly roll sheet pan with parchment paper. Make sure the parchment paper sticks up at least an inch above the sides of the pan on all sides. You’ll use the parchment paper later to lift the cake out of the pan and roll it up. Spray the parchment paper with cooking spray to keep it from sticking.
In a medium-size bowl, whisk the flour, cocoa, baking powder, and salt together. Then set aside.
In a large bowl, combine the egg yolks and sugar and whisk together until well combined. Then add the Cultured Cream, melted butter, and vanilla extract to the bowl and whisk together until well combined.
Add the dry ingredients to the wet ingredients and gently whisk together until well combined, then set aside.
Add the egg whites to a large mixing bowl and whip on high speed until stiff peaks form.
Gently fold about ⅓ of the whipped egg whites into the chocolate mixture to loosen up the batter. Add the remaining egg whites and gently fold together until well combined.
Spread the cake batter evenly into the prepared pan and bake for 10-12 minutes, or until the top of the cake springs back when touched and a toothpick inserted comes out clean. Remove the cake from the oven and immediately lift the cake out of the pan using the parchment paper and place it on the counter.
While the cake is hot, use the parchment paper the cake was baked in and start at the shorter end of the cake to slowly roll the cake up.
Set the cake aside to cool completely. When the cake has cooled and is ready to be filled, make the filling.