Step 1

Pour 1 cup of water (236 ml) into a small saucepan over medium high heat, then mix in 1 cup of sugar (200g) until it dissolves.  Pour it into a shallow container and put in the freezer for 10 minutes to speed up the cooling process.

Step 2

Wash and dry 9 limes and 2 lemons.  Grate the zest of one lime, then mix it with the margarita salt and spread on a plate.  Wedge the lime and run a wedge around the rim of the glass, then twirl the rim in the salt until coated.  Repeat with the remaining glasses.

Step 3

Roll 6 limes on the counter, applying pressure with your hand to soften them.  (Set aside the other three for garnish.)  Cut the rolled limes in half and microwave them on high for 30 seconds to make them easier to juice.  Juice the limes and lemons with a citrus press.  You should have ½ cup of each lemon and lime juice.

Step 4

Blend together all the ingredients except the sparkling water in the blender, then blend in enough crushed ice to make the drink thick and frozen.  You should have nearly 9 cups.  If you have a small blender, do this step in two batches.

Step 5

Pour the sparkling water into the margarita mixture.  It will fizz a little!  Stir until mixed, then carefully pour the margaritas into the prepared glasses.

Step 6

Thinly slice a lime crosswise, then make a small slit in each slice so it sits nicely on the rim of the glass.  Set the lime wheel on the rim of the glass, then serve the margarita immediately.  You can also freeze the drinks in the glasses for up to 2 hours.