First make the Prickly Pear Syrup. Begin by peeling the prickly pears and dicing into chunks. Combine with sugar in a pot over medium heat. Stir until dissolved and fruit has incorporated or is very soft, about 10 minutes. *Note: This will make more prickly pear syrup than you need. You can store it in the fridge in a jar or air tight container for two weeks.
Strain through a mesh sieve to remove pulp and seeds. Blend on highest speed for 60 seconds. Then strain through a fine mesh sieve into a glass or bottle and let cool. Can be made and stored in the fridge up to three days ahead of time.
Fill cups with crushed ice. These are strong and the ice will help balance the drink. Then make the margaritas by combining 4oz of Prickly Pear Syrup with tequila, Grand Marnier and lime juice in a large pitcher. Pour over ice and top with a splash of Topo Chico (optional) and enjoy!