01 -
Place watermelon cubes in a blender or food processor and process until completely smooth.
02 -
Press the pureed watermelon through a fine mesh strainer into a large bowl or 9x13-inch baking dish to remove pulp, collecting the juice.
03 -
Stir granulated sugar and lemon juice into the strained watermelon juice until the sugar dissolves fully.
04 -
Transfer the sweetened juice to the freezer and freeze for 2 to 3 hours, stirring with a fork every 45 minutes to create a granular texture.
05 -
When the mixture is fully frozen, use a large spoon to scrape the frozen watermelon into fluffy slush.
06 -
Spoon the slush into glasses, filling each three-quarters full. Add a small amount of 7-Up or Sprite to each glass and stir gently. Garnish as desired and serve promptly.