- 3 1/2 pounds seedless watermelon
- 3/4 cup pineapple or white grape juice
- 1/2 cup rum or more fruit juice
- 1/3 cup lemon juice
- Sugar
- Cut rind off watermelon and discard. Cut fruit into 1/2-inch chunks.
- Line a 10- by 15-inch pan with plastic wrap. Arrange fruit on wrap in a single layer. Freeze until firm, 1 to 2 hours; if making ahead, transfer frozen chunks to a freezer bag.
- In a blender, combine half the pineapple juice, rum, and lemon juice. Whirl, gradually dropping in half the frozen watermelon chunks, until smoothly pureed. Sweeten to taste with sugar and pour into a pitcher or directly into glasses. Repeat to make a second batch.