Watermelon colors are THE hot pastry trend. Just roll with it.
6 to 8 servings
For the seeds:
¼ cup dark chocolate, finely chopped
For the cake:
4 large eggs, divided, at room temperature
6 tablespoons granulated sugar, divided
3 tablespoons whole milk, room temperature
3 tablespoons vegetable oil
1/2 teaspoon vanilla extract
1/4 cup all-purpose flour, sifted
1 package unsweetened watermelon drink mix (such as Kool-Aid)
3 tablespoons cornstarch
1/2 teaspoon cream of tartar
Red and green food coloring
1/2 cup powdered sugar, for rolling the cake
For the filling:
1 1/4 cups heavy whipping cream
1/4 cup powdered sugar
Make the seeds: Melt the chocolate by microwaving it in 15 second intervals. Place melted chocolate in a piping bag fitted with a fine line tip, or cut the corner off a plastic bag. On a parchment-lined sheet pan, pipe chocolate out to make seed shapes. Set aside to let harden completely, or refrigerate.
Make the sponge cake: Preheat oven to 350 degrees. Line a baking sheet with parchment paper. Dust a tea towel with powdered sugar for rolling.
In a medium bowl, whisk together yolks and 2 tablespoons of sugar until the sugar is dissolved. Whisk in milk, vegetable oil and vanilla until smooth. Sift in the flour, watermelon drink mix and cornstarch and whisk until smooth.
In the bowl of a stand mixer, whip the egg whites until frothy. Add the cream of tartar. Whip at medium-low speed for 2 minutes, then gradually add the remaining sugar. Whip on medium-high for 5 to 7 minutes until stiff peaks form. Fold the egg white mixture into the egg yolk mixture. Divide half into a separate bowl. Tint one bowl of batter with red food coloring until pink, and the other batter with green food coloring until pale green. Remove 2 tablespoons of the green batter and tint darker green. Carefully pour the pink batter onto one side of the pan, and the light green batter onto the other. Use the dark green batter to draw lines on the light green side and use a butter knife or toothpick to pull the dark green color in alternating directions. Tap the pan to remove air bubbles.
Bake in the oven for 12 to 17 minutes, checking that the cake springs back when touched. Run a knife around the edges of the cake to loosen. While the cake is still very warm, flip each cake onto a kitchen towel that is lightly dusted with powdered sugar. Roll into the towel and set aside to cool for 30 minutes to 1 hour.
Make the whipped cream frosting: In the bowl of a stand mixer fitted with a whisk attachment, whip heavy cream until thick. Add in the sugar and continue whipping until soft peaks form.
Assemble: Once the cakes are completely cool, gently unroll from the towel and trim the edges. Spread a layer of whipped cream frosting over the cake. Using the towel as support, roll the cake tightly over itself. Wrap in plastic wrap and refrigerate at least 4 hours or overnight. Cut, and sprinkle with the “seeds” before serving.