Remove the seeds from the watermelon and scoop out the flesh with a baller or cut into small cubes. Place in a punch bowl. Cut the honeydew melon in half. Remove seeds and spongy flesh, then also scoop out the flesh as balls or cut into small cubes. Add to the watermelon mold and sprinkle everything together with the powdered sugar.
Then add a third of the rose wine. Slit the vanilla stalk lengthwise and add it. Leave the mixture to cool for at least 120 minutes.
Before serving, add the rest of the chilled rose wine and the champagne.
If you wish, you can also use Prosecco (from Italy), Cava (from Spain) or sparkling wine (from Germany) instead of champagne.