- In a small saucepan, combine all the ingredients. Bring to a boil and let simmer over medium heat for 5 minutes. Strain through a sieve. Let cool.
- In a 4-cup (1 litre) bottle, combine the ginger syrup, tequila, lime juice and Cointreau (see note).
- When ready to serve, using a blender, finely crush half of the ice at a time with half of the ginger margarita mixture. Serve in margarita glasses.
You can make the ginger margarita mixture up to 2 weeks in advance and keep it in the refrigerator.