Pre-heat the oven to 450°F. Pat the fish dry with paper towels and season simply with salt and pepper. Preheat an oven proof skillet (cast iron is preferred) over medium-high heat. Add heat-tolerant fat to the pan and place the fish in the pan, flesh side down, careful not to crowd pan. Cook flesh side down for 2-3 minutes or until nicely browned. Flip fish over and transfer entire skillet to pre-heated oven. Cook for remaining time (use the rule of thumb for cooking times) in the oven. Remove the skillet from oven (WARNING: the skillet handle will be extremely hot). Place a pat of butter on top. Your fish will be perfectly cooked, crispy on the outside and juicy on the inside.