Fill a cocktail glass with ice and water to chill.

Meanwhile, half-fill a cocktail shaker with ice and add the juice of ½ a lime and ½ an orange, 40ml tequila, 20ml Cointreau, and 10ml cranberry syrup (Cocktail Porter also makes a great cranberry & blood orange syrup). Shake till the shaker becomes cold to the touch. 

Drain the cocktail glass of the ice and water and strain in the cocktail.

Serves 1.