HOT pan, whether cast iron or other is fine. Sear both sides, and if its not done ave the over ready at about 400 degrees. I always cook for 5 so I need to sear fish and put it in a glass pan, get all the fillets seared, and then pop in the over for about 4-6 minutes while I am getting things ready. Comes out piping hot, and perfectly cooked! Had some tonight in fact..mmmmmm i LOVE blacked anything.