Mocha Roll Cake

Mocha Cake Sheet

Prep: Preheat oven to 350°F. Line a 12x17" baking tray with parchment paper cut to size and set aside.
Flour mixture: In a small bowl, stir together cake flour, cocoa powder, and espresso powder. Set aside.
Separate eggs: Separate the egg whites and egg yolks into two large mixing bowls, being careful not to get any yolk in the egg whites. Set the bowl of egg yolks aside.
Egg white meringue: To the egg whites, add cream of tartar. Use an electric hand mixer to beat the egg whites on low-medium speed until they become frothy like cappuccino foam. Add 100g of sugar, one spoonful at a time, mixing in between each addition. After all the sugar has been added, continue beating on medium-high speed until the meringue becomes stiff peaks. Set aside.
Egg yolk mixture: To the egg yolks, add the remaining 50g of sugar. Use the same hand mixer to mix until combined. Add the milk, oil, and vanilla extract and mix until combined. Use a fine mesh sieve to sift the flour mixture into the egg yolk mixture. Mix on low speed until the flour has just combined.
Combine meringue and egg yolk mixture: Add about ⅓ of the egg white meringue into the egg yolk mixture and fold together with a spatula, making sure to scrape the bottom of the bowl. Add the rest of the meringue and fold together until no streaks remain. Again, make sure to scrape the bottom and sides of the bowl where thicker batter can stick. Don't overmix.
Fill pan: Pour the batter into your lined baking tray. Use an offset spatula to spread the batter into the corners and edges of the pan and smooth the batter into an even layer.
Bake: Bake for 13-14 minutes or until the edges are lightly browned and the top of the cake sheet is puffed up.
Release cake: Let the cake cool on a wire rack for only about 5 minutes before running an offset spatula around the edges of the pan to release the cake. Place a wire rack on top of the pan, grip both sides of the pan and rack (with oven mitts), and flip the cake onto the rack. Peel the parchment paper off the cake. Place a fresh sheet of parchment paper on top and flip the cake onto the parchment paper.
Pre-roll cake: While the cake is still warm, roll the cake up with the parchment paper starting from a short end. Let the cake cool completely in this rolled-up log shape.

Espresso Whipped Cream

Whip cream: To a mixing bowl, add the whipping cream, powdered sugar, espresso powder, and vanilla extract. Use a hand mixer to whip until it becomes stiff peaks.
Spread cream on cake: Unroll your cooled cake sheet. Add dollops of whipped cream on top of the cake sheet. Use an offset spatula to spread the cream into a thick, even layer. Leave the last 2" at the end of the cake sheet empty. Save any remaining whipped cream for decoration later.
Roll cake: Roll the cake up in the same way as before. When you get to the end of the roll, place a sheet of plastic wrap next to the cake so that you can roll the cake right onto the plastic wrap. Use an offset spatula to remove any excess cream that squishes out of the seam and push any cream that comes out from the two ends of the roll. Wrap the cake roll in plastic wrap and chill the in fridge for at least 3 hours or overnight to allow the cream to set.
Slice: Before serving, use a serrated knife to cut off about ½" off both ends of the roll to reveal the swirl. Cut the cake into 1-1.5" slices. Pipe any remaining whipped cream on top and garnish with coffee beans (optional).