• Preheat the oven to 350F.

Make the watermelon pattern:

• Beat the butter with an electric mixer until light and fluffy. Add the sugar and beat until combined. Add the eggs whites, vanilla extract and a couple drops of green food coloring and beat until combined. The batter should be a deep green color. Add the flour on low speed.
• Place the batter into a piping bag fitted with a medium-sized, round piping tip.
• Line a swiss roll pan with parchment paper. Pipe squiggles all over the paper, piping in the direction from one short end to the pan to the other.
• Transfer the pan to the freezer and freeze for 30 minutes.

Make the cake batter:

• Beat the 6 egg whites and salt with an electric mixer until soft peaks form. Add half of the sugar and beat until stiff, glossy peaks are formed.
• In a separate bowl, beat the egg yolks and remaining sugar with an electric mixer until pale and doubled in volume. Gradually add the vanilla extract and butter and mix until well combined.
• Add the flour to the batter in 2 additions, alternating with the egg whites. Dye the batter a lighter green than the squiggles and gently fold to combine.
• Pour the batter into the swiss roll cake pan, on top of the pattern. Gently smooth the surface and bake at 350F for 13-15 minutes, until the edges are golden.
• Dust a large sheet of wax paper with powdered sugar. As soon as the cake comes out of the oven, invert it onto the wax paper. Peel off the top layer of parchment paper, place another layer of wax paper on top, then invert again, so that the patterned side is facing down.
• Place two rolled up kitchen towels lengthwise down the center of the cake. This will give the cake support as it cools and encourage it to maintain it’s “ring” shape, vs collapsing and creating an oval shape. Starting at one long end, gently roll the cake up. Wrap in a kitchen towel and cool completely.
• Wrap in a kitchen towel and cool completely at room temperature.

Make the filling:

• Beat the whipping cream with an electric mixer until soft peaks form. Add the powdered sugar, vanilla extract and pink food coloring and beat until stiff peaks form.
• Gently fold the mini chocolate chips into the cream.

Assembly:

• Gently unroll the cake and peel off the wax paper. Spread the filling onto the surface and roll the cake back up again.
• Wrap the cake in plastic wrap and chill in the fridge for 4 hours, or up to overnight.
• Slice off the ends to create a clean look and enjoy!