1-First, cut the top and bottom off the watermelon to create flat ends and make it stand upright. Then, carve away the rind in downward strips until only the red, ripe center remains, shaping it roughly like a cake by trimming the sides and top.

2-Next, beat 2 1/2 cups heavy whipping cream on high with an electric mixer until it begins to thicken, gradually adding 1/4 cup sugar one tablespoon at a time.

3-After that, add the seeds from one vanilla bean and continue beating until the cream is thick and spreadable. Pat the watermelon surface dry to remove excess moisture, then spread the whipped cream evenly over it.

4-Finally, use a melon baller to scoop round pieces from the reserved watermelon ends and place them on top, garnishing with mint sprigs if desired, before storing the cake in the refrigerator until serving.