Slice the melons so you get slabs that are 1- 1.5 inches thick. You’ll need 2 watermelon layers, 1 honeydew, and 1 cantaloupe. Set the rest of the fruit to the side to use later.
Use a cookie cutter to cut out the middle flesh and seeds from the center of the cantaloupe and honeydew slabs.
Stack the slices on each other with the largest on the bottom (typically the watermelon slab is the largest).
Use a sharp knife to cut a circle around the stacks. In one step, you are removing the rinds and creating the layers of the watermelon cake that are all the same size around.
With one watermelon slice on the bottom and the other on top, stack the fruit slabs to make sure they are all the same size.
In a large bowl or the bowl of a standing mixer, combine the cream, vanilla, and sugar. Whip on medium speed until stiff peaks form.
Do not over beat whipped cream mixture or it will turn to butter.
Place the first slab of watermelon on a serving platter or cake plate to form the bottom of the cake. Top with a layer of whipped cream.
On the whipped cream layer, stack the cantaloupe ring, forming the second cake layer. Add a thick pool of whipped cream to fill the empty center and then another layer of whipped cream on top of the cantaloupe.
Repeat the process with the honeydew, filling the center solidly with whipped cream.
Top with the final slab of watermelon and mound the remaining whipped cream on top.
Use an offset spatula to spread the remaining whipped cream down the sides of the cake, frosting the cake completely.
Use a melon baller on the remaining fruit to scoop out balls to place on top of the cake, along with the berries.
Decorate your fresh fruit cake. You may like to garnish with some mint leaves or additional berries.