Prepare the Ling Cod by patting the fillets dry and seasoning with Salt and Freshly Ground Pepper.
Heat cast iron skillet (or other heavy bottom pan) over medium high heat. Add a bit of butter or ghee to hot pan. Heat until bubbly.
When pan is hot, and butter is bubbling, add your seasoned fillet/s to the pan. Be patient while you create a hard sear on the bottom of the fish.
After about 4-5 minutes (depending on the thickness of the fish), gently lift the fish to check sear. When looking at the end/edge, you will also notice that the fish is about halfway cooked through. Once nicely seared, gently flip over with a fish spatula to sear the other side.
Once you have flipped the fillet, spoon the sauce over the fish as it continues cooking through, about 3-4 more minutes, depending on the thickness.
Once done, remove to plate, and spoon a bit more sauce over the fish before serving.