Place fish on some parchment paper that is longer than the fish, in a roasting pan or baking dish.
ZI then fill the cavity with a bunch of very thinly sliced onion.
Tonight I had a bunch of fresh parsley, so I chopped that up and added it in.
Now, most recipes say to use parboiled potatoes, but I usually just slice raw ones up quite paper thin. The potatoes help absorb all the juices.
Add butter inside and out.
Wrap fish up in parchment paper (I'm pretty sure I did this the wrong way tonight) and bake in a 350F oven until flaky. I put ours in for 40 minutes, but continue to check until it's done.