Combine all in a small saucepan, bring to the boil. Turn down heat, simmer for two minutes. Remove from heat and allow to cool.
Whizz the mint leaves with the sugar in a food processor until combined.
tip into a bowl and set aside.
Whizz all the ingredients together in a food processor, you might need to scrape the sides of the bowl as the basil will clump together.
Once all combined tip onto a baking tray and spread out evenly to dry.
To make the margarita, start by rimming the glasses with the lime & basil salt.
Using a wedge of lime, moisten the rim of the glass. Dip the glass into the basil salt, turn up right and set aside to dry whilst making the margarita.
Whizz the watermelon, strawberry juice, simple syrup, ice, tequila, lime juice & zest in a blender until the ice is crushed.
Pour into the salt rimmed glasses, garnish with lime wedges, a watermelon wedge and a teaspoon of the mint sugar.