Place 2 fillets in the center of each sheet of aluminum foil.
Mix the clarified butter and lemon juice well and evenly distribute over the 4 sets of fillets.
Salt and pepper the fillets to your liking and top with several rings of onion.
Bring up the long sides of the foil over the fillets and tightly seal together. Fold in each of the ends several times to make the pouch air tight.
Put the pouches on the grill, on med-high heat for 15 - 20 minutes. Fillets will be tender and flakey when done. Serve with new potatoes (cooked the exact same way) and grilled corn cobs! Oh and lots o lemon too!