1. Combine first 4 ingredients and 1/4 teaspoon kosher salt in a small bowl. Cover and set aside.
2. Rub steaks on both sides with remaining 1/4 teaspoon kosher salt and coarsely ground black pepper. Let stand at room temperature 30 minutes.
3. Grill steaks, covered, over medium-high heat (350° to 400°) for 7 minutes on each side or until desired degree of doneness. Top each steak with a dollop of seasoned butter.