Before you start, place the glass in the freezer for about 20 minutes.
This will keep your drink cool.
Wash and juice the lime, add rum and a few drops of stevia.
You can optionally add a few drops of lime, lemon or orange extract, preferably PG-free.
You can read more about food extracts here.
Place the ice in the blender and pulse until crushed.
Remove the glass from the freezer, fill with the crushed ice and add the lime mixture.
Serve with a piece of lime.
Note: You can alternatively use a shaker.
Just place everything inside, shake and strain the mixture into the cocktail glass.