To a jar (use something with a tight-fitting lid if preparing this ahead of time - see Notes below), add the tequila, Cointreau, simple syrup, and fresh lime juice.
Run the cut edge of a lime wedge around the rim of each glass and dip the rims into a small plate of coarse salt.
Add ice to prepared glasses. Give margarita mix a good stir to combine, then divide amongst the glasses. Top with Prosecco. Give a quick stir to combine each individual glass, and then taste test. Adjust for individual tastes by adding more simple syrup for sweetness or lime for tartness. Add lime garnish. Enjoy!
