Light a grill or preheat a grill pan. In a small bowl, combine the butter, garlic, lime zest, lime juice and a pinch of salt. In another bowl, combine the paprika, cumin and chipotle powder with 1 1/2 teaspoons of kosher salt. Rub the mixture all over the steaks.

Oil the grate and grill the steaks over moderately high heat, turning once, until slightly charred and medium-rare, about 12 minutes. Transfer the steaks to plates and top with the lime butter. Let the steaks stand for 3 to 4 minutes before serving.