This America's Test Kitchen recipe pulls no punches: it calls for steeping the citrus and sugar for a full 24 hours. If you didn't plan your partying that far in advance (and really, who does), four hours will do; if this is all last minute, just omit the zest and you're good to go.
Makes 1 quart (4 to 6 servings)
4 teaspoons grated lime zest
1/2 cup lime juice from 2 to 3 medium limes
4 teaspoons grated lemon zest
1/2 cup lemon juice from 2 to 3 medium lemons
1/4 cup superfine sugar
pinch table salt
2 cups crushed ice
1 cup 100 percent agave tequila, preferably Reposado
1 cup Triple Sec
Combine lime zest and juice, lemon zest and juice, sugar, and salt in large liquid measuring cup; cover with plastic wrap and refrigerate until flavors meld, 4 to 24 hours.
Divide 1 cup crushed ice between 4 or 6 margarita or double old-fashioned glasses. Strain juice mixture into 1-quart pitcher or cocktail shaker. Add tequila, Triple Sec, and remaining crushed ice; stir or shake until thoroughly combined and chilled, 20 to 60 seconds. Strain into ice-filled glasses; serve immediately.