"Once you see all the lemons and limes cooked and fragrant on the grill, you'll believe the extra steps to this limeade are worth the wait. The grilling jumpstarts the flavor out of the citrus, so that every sip is bracing, refreshing, and uniquely delicious."
Preheat grill for medium heat and lightly oil the grate.
Pour sugar into a saucepan; press halved lemons and limes cut-side down into the sugar.
Set the saucepan with remaining sugar on grill; stir in 2 cups of water and whisk over the heat until dissolved into a syrup. Let cool.
Place lemon and lime halves sugared-side down on grill and cook until browned, about 5 minutes.
Place lemon and lime slices on the grill; cook until browned, 30 to 60 seconds on each side.
Juice halved lemons and limes into a large pitcher. Add syrup and 2 cups water to the juice, 1/2 cup at a time, until the limeade achieves desired sweetness. Pour limeade into glasses filled with ice; garnish each glass with a grilled citrus slice.