In a small to medium-sized jar or bowl, add the tequila, Cointreau, simple syrup, and fresh lime juice. Prepare this mixture at least a couple hours prior to serving the margaritas, and place in refrigerator to chill.This recipe will make 4 medium-sized margaritas or 6 smaller ones. Gather 4 to 6 medium or small glasses and get started! If salting the rims of your glasses, run the cut edge of a lime wedge around the rim of a glass and dip the rim into a small plate of coarse salt. Repeat with remaining glasses.Add ice to prepared glasses and divide chilled tequila mixture amongst the glasses. Top with Prosecco. Give a little stir to combine, and then taste test. Adjust for individual tastes by adding more simple syrup for extra sweetness and lime for tartness, plus extra tequila for those who like a bit more tequila bite. Squeeze a lime wedge over the top and add another one to the rim of the glass. Enjoy!