How to make Watermelon Sponge Cake

By Eva Kosmas Flores

Watermelon Sponge Cake
Photo by Eva Kosmas Flores

It’s getting close to the hottest part of the summer, and nothing cuts through the heat like a ripe slice of watermelon. I grow a few kinds every year out in the garden, and it’s so much fun to compare the colors, sizes, and flavors of the different watermelon varieties. The overall flavor tends to be the same, but some varieties are definitely sweeter than others, with my favorite being the Criss Cross watermelon varietal. And while eating raw watermelon in the summer is very satisfying, when you have 30 pounds of it on your hands you start to look for a little variety in preparation, and that’s where this little sweet comes into play. This recipe transforms everyone’s favorite summer fruit into cake form with a cold-pressed watermelon syrup that’s incorporated into a tasty watermelon curd. It’s the best way to have your cake and eat it, too!

Watermelon Sponge Cake

Ingredients for Cake
6 eggs, separated
1 cup sugar
1/4 cup water
1 cup flour
1/2 teaspoon cream of tartar
1/4 teaspoon salt

Cold Press Watermelon Simple Syrup
1/2 cup watermelon puree
1 cup granulated sugar

Ingredients for Watermelon Curd
1/2 cup plus 2 tablespoons sugar
5 tablespoons butter
2 eggs
1 egg yolk
3 tablespoons watermelon syrup
4 drops pink food coloring (optional)

Watermelon Whipped Cream
1/2 cup plus 2 tablespoons sugar
5 tablespoons butter

First, make the watermelon syrup. Mix together the watermelon puree and sugar in a medium sized bowl. Cover and refrigerate for 4 hours or overnight. Strain the syrup though a mesh sieve to remove any large particles and seeds. Reserve the syrup in a separate bowl and cover and refrigerate it until use. (You will have some left over after the recipe, I recommend using it as a mixer for cocktails or stirring it into some fresh lemon juice for a watermelon lemonade).

To make the watermelon curd, cream together the butter and sugar until smooth. Add the eggs, one at a time, and then the yolk, and mix until blended. Pour the mixture into a small thick-bottomed saucepan and cook over low heat whisking constantly, until the temperature of the mixture reaches about 170 degrees Fahrenheit with a candy thermometer, or until the mixture has thickened significantly (it usually takes between 8 and 15 minutes depending on your heat level and stovetop). Remove from heat immediately and continue whisking for the first few minutes so the mixture doesn’t cook onto the bottom of the hot pan. Allow to cool to room temperature, then whisk in 3 tablespoons of the chilled watermelon syrup and the optional pink food coloring until incorporated. Cover and place the curd in the refrigerator until use.

Watermelon Sponge Cake

In a separate bowl, beat the egg whites with a whisk attachment at high speed until foamy, then add the cream of tartar and salt and continue beating until stiff peaks form, but do not over beat. Fold the egg white mixture into the batter until incorporated, then evenly distribute the batter between the three cake pans. Place in the oven and bake for 30-40 minutes or until the cakes turn golden brown on top. Turn the oven off and open the oven door halfway. Allow the cakes to cool in the oven for 30 minutes before running a knife around the edge of each pan to loosen the cakes grip. Flip the pans over onto a wire rack and remove the pan. Allow the cakes to cool completely, then trim the crust.

While the cakes are baking and cooling, you can prepare the whipping cream. Beat the heavy cream and 2 tablespoons of the watermelon syrup with a whisk at high speed until thick and fluffy, but take care not to over beat. Cover and refrigerate until use.

To assemble, place a layer of the cake on the serving surface. Spread a smooth layer of whipped cream on top of the cake, and then spread a layer of the curd on top of the whipped cream. Repeat until all of the toppings and cake layers are used. Serve immediately and refrigerate and leftovers.

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