In a small saucepan, sprinkle gelatin over cranberry juice; let stand for 1 minute. Heat over low heat, stirring until gelatin is completely dissolved.
Place watermelon in a blender; cover and process until smooth. Add sugar and gelatin mixture; process until blended. Pour into an 8-in. square dish. Freeze for 1 hour or until edges begin to firm. Stir and return to freezer. Freeze 2 hours longer or until firm.
Just before serving, transfer to a food processor; cover and process for 2-3 minutes or until smooth.
Could use lemon or lime juice or lemonade.
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