3ounces(6 tablespoons) freshly squeezed lime juice
To make the syrup: Bring water to a boil in a small pot or saucepan. Add the hibiscus flowers and sugar, lower the heat to medium, and simmer steadily until the sugar dissolves and the syrup has thickened slightly, about 5 minutes. Strain the mixture through a sieve, and let cool. This makes about 1 ½ to 1 ¾ cups of syrup and keeps up to 1 week in the fridge.
To make a single margarita: Combine hibiscus syrup, tequila, Cointreau, and lime juice with ice in a cocktail shaker. Shake well, then strain into a salt-rimmed ice-filled glass and serve immediately.
To make a pitcher of margaritas: Combine the syrup, tequila, Cointreau, lime juice, and 2 cups of ice in a pitcher and stir very well, at least 1 minute. It’s important to stir for a full minute so some of the ice dissolves. Pour the mixture into 6 salt-rimmed ice-filled glasses and serve immediately.
To rim your glasses with salt, gently rub a lime wedge along the rim of your glass (you can also use a bit of water to wet the rim). Add some kosher (coarse) salt to a plate and then press the wet rim of the glass against the salt, carefully rotating the glass until there is an even coating around the circumference.
You may garnish with hibiscus flowers in syrup if you'd like! They are beautiful and delicious, but even a wedge or slice of lime will do.
Shaking these hibiscus margaritas vigorously will yield some foam on top. You can either leave it (as I typically do), carefully skim it from the glasses with a spoon, or pour each drink into a measuring cup with a spout first to skim and then transfer the foam-free mixture to a glass. To be honest, the foam never bothers us, but you do you. If you make this in a pitcher they shouldn't get foamy.
If you like your hibiscus margaritas sweeter you can increase the amount of sugar in the recipe, or add some agave nectar when shaking them up.