Ingredients

For the rim:

• 1 teaspoon Diamond Crystal kosher salt
• 1/2 teaspoon Tajín Clásico seasoning
• 1 lime wedge

For the cocktail:

• 2 cups cubed seedless watermelon (about 10 ounces)
• 3 ounces vodka
• 3/4 ounce freshly squeezed lime juice (about 1 1/2 small limes), plus more as needed
• 1/2 ounce agave nectar
• Ice
• 2 watermelon wedges, for garnish (optional)

Rim the glasses:

1. Mix 1 teaspoon Diamond Crystal kosher salt and 1/2 teaspoon Tajín seasoning together on a small, flat plate; spread into an even layer. 
2. Run 1 lime wedge over the rim of 2 highball or old-fashioned glasses to moisten. Invert the glasses into the salt, turning it as needed, to coat the rim.

Make the cocktails:

1. Blend 2 cups cubed seedless watermelon in a blender until smooth. Strain the juice through a fine-mesh strainer into a liquid measuring cup. You should have about 1 cup of watermelon juice. Strain the juice again into a cocktail shaker. Add 3 ounces vodka, 3/4 ounce lime juice, and 1/2 ounce agave nectar.
2. Fill the glasses with ice and the cocktail shaker halfway with ice. Seal the shaker and shake the cocktail vigorously until the outside of the shaker is frosty, about 20 seconds. Pour through a strainer into the glasses. Taste and stir in more lime juice if needed. Garnish each with a watermelon wedge if desired.