1. Heat 1 tablespoon salted butter in a cast-iron or nonstick skillet over medium-low heat. 2. Press the sandwich slightly and place it in the skillet. Cook until golden on the bottom, 3 to 5 minutes. 3. Flip, adding more butter to the pan if needed, and cook until the other side is golden and the cheese melts, 3 to 5 more minutes.