Place the cod fillet on a parchment paper-covered baking sheet. Top with 3-4 tablespoons of butter, equally spaced on the cod.
Slice the lemon. Place it on top of the tablespoon of butter.
Bake in a preheated oven for 25-30 minutes or until the internal temperature reaches 145 degrees F with a meat thermometer. If the cod pieces are thinner, it will take less time. Likewise, if the cod is thicker, it will take longer.
Squeeze the oven-roasted lemon slices over the cod fish. Pour a bit of the melted butter lemon sauce over the baked cod. Top with fresh herbs if desired.
Serve immediately with homemade tartar sauce.
Notes
Note 1: Cod filets will vary greatly in size. The smaller and thinner pieces will require less butter, lemon slices, and cooking time. The larger, thicker pieces will require more time. Cod must also be defrosted before cooking. Defrost overnight in the refrigerator. Note 2: May only need one lemon, depending on how many pieces of cod are being used. Store leftovers in an airtight container in the refrigerator.