Frozen Watermelon Mint Gin Fizz

To make the simple syrup: Combine all ingredients in a small sauce pan. Bring to a boil, making sure to stir until the sugar has dissolved. Once it has boiled and combined, remove from heat and allow to cool to room temperature. Then, either strain the mint leaves or use your stick blender to puree them into the syrup.
Juice approximately half a watermelon. This can be done with a juicer or by cutting into chunks and using a food processor or blender. I used my stick/immersion blender. After it is pureed, run through a mesh strainer/sieve to remove any pulp or seeds. A little pulp is fine, but try to get it as close to juice as possible.
Combine simple syrup and watermelon juice with 1 cup of gin (or vodka, if you prefer). Pour into 2 plastic quart containers, leaving at least an inch of room at the top, and freeze over night.
To assemble: Remove the frozen quart container from the freezer and, using a spoon, shave it and scoop into a glass. Then add a shot of gin or vodka to the glass, plus enough soda water to cover the slush. Stir until everything is combined and the drink has a slurpee-esque consistency. Add a straw, garnish with a lime if desired, and serve. This recipe should make about 12 generous servings.