Grilled-Citrus Margaritas

Light a grill. Grill the halved limes and lemons over high heat, cut side down, until lightly charred and juicy, about 5 minutes. Transfer to a plate to cool. Juice the limes into one measuring cup, and juice the lemons into another measuring cup; you should have about 4 ounces of each juice. Using the lime wedge, moisten half of the outer rim of 6 rocks or margarita glasses and coat lightly with salt, then fill each glass with ice. Fill a pitcher with ice and add the tequila, simple syrup and 3 ounces each of the lime and lemon juices. Stir well and strain into the prepared glasses. Using tongs and working with one at a time, hold an orange twist directly over the flame until just singed around the edges. Garnish the margaritas with the flamed twists and serve.