For this recipe you need a 52-ounce pitcher.
First, add the fresh lime juice and then the Cointreau.
Have a taste¬-it should still be a bit tart.
You can add a little more Cointreau but not much.
Adjust the sweetness with a little agave syrup (two parts agave nectar, one part water) or simple syrup (one part sugar, one part water) but don't use more Cointreau, which would change the balance of the drink.
Add the tequila and taste.
The mixture should still be intense, because you haven't added any ice yet.
When a guest wants a drink, pour 3 ounces of the mix into a shaker and fill with ice.
Shake, and strain into a stemmed Margarita or cocktail glass with a half-salted rim or a rocks glass filled with fresh ice.
Garnish with a thin wheel of lime.
If you have a large shaker or a gallon jar with a screw-top you can shake a whole bunch of drinks at the same time.