Place the salt in a shallow dish. Dip the glass rim side down, into the salt and rotate it around until the rim is lightly coated. Fill the glass with ice. Set aside.
Add a heaping ¼ cup of watermelon and the basil leaves to a cocktail shaker or glass with a lid.
Muddle together using a muddler or wooden spoon, until the watermelon and basil has broken up.
Add the agave, lime juice and tequila to the shaker.
Shake aggressively for 30 seconds.
Pour in the salt-rimmed glass over ice. Garnish with watermelon slices and fresh basil leaves. Enjoy!
Notes
If you don't have a muddler you can use a wooden spoon to mash/squish the watermelon and basil.
Use the sweetener of your choice in place of agave (simple syrup, maple syrup or honey).
ALWAYS use fresh lime juice! Not the bottled juice. Fresh is best. I find that it takes about 1 ½ limes for 1 ounce of lime juice.
Try using watermelon tequila for a flavor boost. Alternatively if you don't like tequila you can try substituting in vodka, rum or gin.
Try using tajin or sugar on the rim of the glass in place of salt.