Place powdered sugar and salt in a small bowl, and mix in the lemon juice. Continue stirring until powdered sugar has dissolved. Before opening the can of coconut milk, shake the can of coconut milk up really well so that there is no separation inside. Mix shaken coconut milk into lemon mixture.
Pour mixture into the frozen inner core of the Slush and Shake Maker. Wait a minute of two, and then scrape the walls of the cup with the included plastic spoon to remove the iced mixture. Continue scraping and stirring until your slushy is the desired consistency.
This can also be made in a freezer safe container placed in the freezer, stirring occasionally until frozen. Or, try a compact ice cream machine, an ice cream bowl, or place the mixture in a regular ice cream maker and mix until desired consistency.