Hot Chocolate and Marshmallow Cake Roll

Ingredients

• For the cake:
• Baking spray
• 1 cup unsweetened cocoa powder
• 1/2 cup plus 2 tablespoons sifted cake flour
• 3/4 cup sugar
• 1 1/2 teaspoons baking powder
• 3 large egg yolks, at room temperature
• 2 teaspoons pure vanilla extract
• 1/4 cup hot water
• 4 large egg whites, at room temperature
• 1/2 teaspoon salt
• For the filling:
• 1 tablespoon water
• 1 teaspoon unflavored gelatin
• 2 ounces cream cheese, softened
• 1 cup confectioners' sugar
• 1/4 teaspoon salt
• 2 cups heavy cream, chilled
• 2 cups mini-marshmallows
• For the hot chocolate sauce:
• 1 cup heavy cream
• 6 ounces bittersweet chocolate, chopped
• 1 teaspoon pure vanilla extract

Directions

1. For the Cake: Set a rack in the center of the oven and heat it to 325 degrees F. Mist a jelly roll pan lightly with baking spray. Add a sheet of parchment, spray it lightly again, then dust the pan with 1/4 cup cocoa powder, tilting and tapping so it coats evenly. Shake out anything extra.
2. Sift the sifted cake flour, 1/2 cup cocoa powder, 1/2 cup sugar, and baking powder together. Sift the mixture a second time, then transfer it to a large bowl.
3. In a medium bowl, use an electric mixer on medium speed to beat the egg yolks, oil, and vanilla until smooth. Add this to the flour mixture and whisk until it comes together; it will be thick. Pour in the hot water and whisk until the batter is smooth.
4. In a clean, completely dry mixing bowl, beat the egg whites and salt with the whisk attachment on medium speed until they hold soft peaks, about 2 minutes. Turn the mixer up to medium-high and add the remaining 1/4 cup sugar a little at a time; keep beating until the peaks are stiff, 1 to 2 minutes longer. Mix 1/3 of the egg whites into the batter until fully blended. Use a rubber spatula to carefully fold in the rest of the egg whites.
5. Transfer the batter to the prepared pan and smooth it into an even layer. Bake until the cake is pale golden on top and bounces back lightly when pressed, about 15 minutes.
6. While the cake is in the oven, sprinkle the remaining 1/4 cup cocoa powder over a clean, dry kitchen towel.
7. Loosen the edges of the hot cake with a knife. Invert the cake onto the cocoa-dusted towel. Beginning with the short end, roll the cake up inside the towel, then set it seam-side down on a cooling rack. Let it cool completely, about 45 minutes.
8. For the Filling: After the cake has cooled, stir the water and gelatin together in a small bowl. Microwave until the gelatin is dissolved, about 20 seconds. Let it come to room temperature, about 5 minutes. In a large bowl fitted with the whisk attachment, beat the cream cheese, confectioners' sugar, vanilla, salt, and dissolved gelatin on medium speed until airy and fluffy, about 2 minutes. Lower the speed, pour in the cream, and beat until combined. Raise the speed to medium and beat until soft peaks form, about 2 minutes. Fold in the marshmallows.
9. To Assemble: Gently unroll the cake, keeping it on the towel. Spread the marshmallow cream filling over the cake, leaving a 1/2-inch border around every edge. Starting at the short end, roll the cake back up slowly and carefully, this time without rolling the towel into it. Peel away the parchment. Set the cake seam-side down on a baking sheet and chill until the filling is firm, about 1 hour.
10. For the Sauce: Warm the cream and salt in a small saucepan over medium-low heat until it reaches a simmer. Alternatively, heat the cream in a microwave-safe container. Put the chocolate in a medium bowl. Pour the hot cream over the chocolate and stir until the chocolate has fully melted. Stir in the vanilla and salt.
11. Cut the roll into slices and serve with the chocolate sauce.