Japanese Style Chocolate Chiffon Cake

Line an 8 X 12″ rectangular cake pan with parchment paper.
In a small saucepan, heat the milk and cocoa powder on medium heat until the powder is fully dissolved. Do not let the milk come to a boil. Keep stirring continuously while breaking down big clumps of powder. Once fully dissolved, set the chocolate milk mixture aside to cool.
Preheat oven to 325°F.
In a large mixing bowl, add sugar, baking soda, the first portion of cream of tartar, and salt. Sift in the cake flour and stir to combine.
Create a well in the center. Inside it, add yolks, oil, vanilla extract, and chocolate milk mixture.
Stir to combine until fully incorporated, but do not over mix. Set this chocolate-flour mixture aside.
In a clean and dry, non-plastic mixing bowl, whip egg whites on slow speed until frothy, then add the second portion of cream of tartar.
Increase speed to medium. Once the whites become opaque and bubble size has tightened up, add sugar a little bit at a time.
Increase speed to medium-high and whip until stiff peaks form. You’ve now made a meringue.
Gently fold ⅓ of the meringue into the chocolate-flour mixture to get it moving. Once incorporated, fold in the rest of the meringue. Do not stir. Use batter immediately.
Dab a bit of the batter onto the sides of the parchment paper to keep corners together. Dab a little more onto the paper and stick it to the pan to prevent the parchment paper from tipping over into the cake batter.
Pour into the lined cake pan from one spot, and spread out the batter evenly with an angled spatula.
Tap the pan on the counter to release large air pockets.
Bake for 14-16 minutes at 325°F until a skewer pulls out clean and the cake springs back in the center.
Let cool for 5 minutes in the pan before removing.
Place a cooling rack over the cake pan.
Flip the cake over onto the rack and gently remove the paper. The side facing up will eventually become the top of the cake roll. Try to remove as much of the “skin” as possible since the cake will look better with exposed crumbs. Let it sit on the cooling rack for 5 minutes.
Place a piece of new parchment paper on top.
Flip the cake over and start rolling, allowing the parchment paper to be in between the folds. This will prevent the cake from sticking to itself. It’s important to roll the cake before it cools completely; otherwise, it will crack while rolling.
Let it cool in this wrapped condition while making the chocolate whipped cream.
Light and Airy Chocolate Whipped Cream

Place a mixing bowl and beaters in the freezer to chill. It will help the cream whip better.
Chop up chocolate into small pieces.
Place chocolate in a small pot along with the cream.
Heat over medium heat until the chocolate is fully melted. Do not bring to a boil.
Let cool to room temperature, then place in the fridge to chill. Check on it every 10-15 minutes and give it a gentle stir. It should be chilled before whipping, but do not let it cool for too long as it will become too stiff to whip.
Place the chocolate and cream mixture in the chilled mixing bowl, then beat on low speed, slowly increasing to medium. Stop when it starts to get stiff. Do not over whip.
Assembly

Very carefully unroll the cake.
Gently add one even layer of the chocolate whipped cream onto the unrolled cake.
Very gently roll the cake back up using the parchment paper to help push the cake onto itself. This will help prevent cracking. To further prevent cracks, add more cream along the short edge that is folded first and do not try to roll the cake too tightly. Cut off the sides before placing on a presentation plate. Enjoy!