1. Cut the watermelon in half. Using a spoon or melon baller, remove a portion of the watermelon from the center of one half, creating a well large enough to hold the cream.**
2. Cover half the watermelon in cling wrap. Place it into the freezer and freeze overnight, or until completely frozen.
3. Remove the frozen watermelon from the freezer. Remove the cling wrap. Pour the cold heavy whipping cream into the well in the center. If using sweetened condensed milk, vanilla, or salt, add them now.
4. Using a sturdy spoon, scrape the frozen watermelon flesh surrounding the well. As the frozen watermelon shavings fall into the cream, stir to combine.
5. Continue scraping and mixing until the cream becomes thick, fluffy, and pale pink, with the texture of a soft frozen dessert.
6. Serve immediately directly from the watermelon shell, or scoop into serving dishes.
7. Garnish with watermelon cubes, lime zest, fresh mint leaves, or a drizzle of condensed milk.
8. For a firmer texture, place the mixed dessert in the freezer for 10-15 minutes before serving.

**Leave plenty of watermelon around the sides and bottom; you are not hollowing out the watermelon.( Enjoy the removed watermelon or reserve it for another use.)