1 lime, juiced
1/2 lemon, juiced
2 tablespoons white sugar
2 (1.5 fluid ounce) jiggers reposado tequila (such as Jose Cuervo® Gold)
1 cup ice cubes, or as needed
salt as needed
1 teaspoon brandy-based orange liqueur (such as Grand Marnier®), or to taste (optional)
Squeeze lime juice and lemon juice into a cocktail shaker; top with sugar. Pour tequila over sugar mixture and add ice. Cover shaker and shake. Allow shaker to rest for 1 to 2 minutes.
Spread salt onto a plate. Rub the lemon around the rim of the margarita glass and dip the rim into the salt to coat. Pour margarita into glass and top with brandy-based orange liqueur.