Place the ice, tequila, syrup, and lime juice in a blender.
Blend and pour into the two prepared margarita glasses.
*Spearmint sugar can be made the week before: Add 3 tablespoons freshly chopped spearmint leaves to 1 cup sugar. Stir to combine. Place in a tightly sealed jar. Every few days shake the sugar. After 1 week, separate the spearmint leaves from the sugar. Use immediately or store the sugar for future use.