Preheat oven to 375
Peel and slice onion and place in the bottom of a 9x13 pan
Layer cod fillets over top and season with sea salt, pepper and grated garlic, fresh or ground dill and slices of lemon with peel, add butter.
Add one cup of vegetable broth or stock and cover with a lid or foil wrap.
Bake in a 375 degree oven for 30-40 minutes or until fish is cooked through and flakes easily with a fork. Cooking time will depend on the thickness of your fillets. If they are thin, reduce the time.
Serve with some chopped fresh dill and fresh lemon if desired. Spoon pan sauce on top.