Pre-chill a tumbler with crushed ice. Crush half the passion fruit and the cane sugar in a mixing glass until the juice is clearly visible. Then add the Limón de la Casita and the syrup. Fill a Boston shaker with ice, place the mixing glass on top and shake vigorously. Strain the cocktail into the pre-chilled tumbler glass.
Every passion fruit syrup is different, so start with 0.5cl of passion fruit syrup and increase to a maximum of 2cl of passion fruit syrup.