1. For the watermelon juice, place roughly 2 cups of cubed watermelon (peeled and seeded) in a blender or food processor. Pulse until completely smooth. Pour the mixture through a fine-mesh strainer into a bowl or cup. Place in the fridge to chill. Chill all other ingredients as well.
2. Fill a shaker with ice and add the watermelon juice, grapefruit juice, vodka/gin, and simple syrup. Shake vigorously for a few seconds to mix and chill the ingredients.
3. Rim two glasses with coarse salt and fill with ice. Divide the mixture between the two glasses and garnish with frozen watermelon wedges, grapefruit slices, and even a sprig or two of mint, as desired. Serve immediately!

NOTE:

1. Simple syrup is optional here. I found that the drink still needed a little sweetness, so I added it a tablespoon or so at a time until I got it where I wanted it. If you’re using really sweet watermelon, though, you may not need any syrup at all. It’s definitely a preference-based thing!
2. To make simple syrup, combine equal parts sugar and water in a small saucepan. Bring to a boil and then simmer for a few minutes until the sugar is completely dissolved. Cool completely and then store in an airtight container in the fridge. Use as needed!