Place the salt and sugar on a small shallow plate and mix. Run a lime wedge around the rim of a highball or Collins glass to moisten it. Dip the rim into the salt-sugar mix, rotating to coat evenly. Set the glass aside.

Extract passion fruit pulp

Cut the passion fruit in half and scoop the pulp (seeds and juice) into a small bowl. If you prefer a smoother drink, press the pulp through a fine-mesh sieve with the back of a spoon to separate juice from most seeds, reserving about 1 tablespoon of seeds/texture for visual interest.

Mix base

In a cocktail shaker or mixing glass, combine 2 oz blanco tequila, 0.5 oz fresh lime juice, 0.5 oz agave syrup and the prepared passion fruit pulp/juice. Add several ice cubes (enough to chill) and shake vigorously for 10–12 seconds to combine and chill.

Assemble the cocktail

Fill the rimmed glass with ice cubes (about 1 cup). Strain the shaken mixture into the glass over the ice. Top with 3 oz chilled grapefruit soda (or 2 oz fresh grapefruit juice + 1 oz club soda) and gently stir once to integrate without flattening the soda.

Garnish and serve

Garnish with a thin grapefruit wheel or lime wedge and a mint sprig if using. Serve immediately with a straw or stirring stick.

Notes

Adjust sweetness by increasing or decreasing agave syrup. If using fresh grapefruit juice + club soda, use freshly squeezed juice and add soda last to preserve effervescence. For a frozen variation, blend the same ingredients with 1 cup crushed ice until smooth.