The whole scenario goes off the rails when you bite into a piece and it turns out of be spoiled. Unlike other fruits, it can be hard to discern at a glance when watermelon isn't good any longer.

Turn off the heat and let cool. Peel and coarsely chop the watermelon. You should have about a quart of watermelon pieces. Purée the watermelon, leaving chunks if you like, as long as they’re ...