2/3 cup fresh lime juice
1/4 cup sugar
1 cup 100% agave tequila
1/2 cup Cointreau
2 cups fresh blood orange juice (it takes me about 18 oranges!)
Cava or champagne, to taste
A lime half for moistening the glass rims
Coarse (Kosher) salt
Ice cubes (you’ll need about 6 cups—small ones are best)
Make the base. In a large pitcher, stir together the lime juice, sugar and 3/4 cup water until the sugar has dissolved. Add the tequila, Cointreau and blood orange juice. Cover and refrigerate until chilled, about 1 hour.
Shake and serve. Moisten the rims of three martini or margarita glasses with the cut side of a lime half. Spread coarse salt on a small plate, then upend the glasses into the salt to crust the rims. Fill a cocktail shaker about 3/4 full of ice and measure in 1 1/2 cups of the margarita for 3 drinks. Cover and shake for about 15 seconds to thoroughly chill the mixture. Strain into the prepared glasses, top with champagne, and serve. Serve the rest of the pitcher accordingly.