Empty coconut milk into a saucepan and add agave nectar, slightly crushed kaffir lime leaves, if using, and salt. Turn heat to low and stir using a wooden spoon just until coconut solids are completely melted into the liquid. Remove from heat and continue to muddle kaffir lime leaves, if using, about twenty seconds. Add lime juice and stir. Taste and adjust sweetness, salt, and acid as desired.

Bring to room temperature. Prepare cocktail shaker with ice, add desired amount of tequila and infused coconut kaffir lime mixture, shake, and serve over ice. Garnish with kaffir (or regulalime zest and extra salt, as desired.