1: Heat 3 inches of oil in a dutch oven or cast iron.
2: Dry the cod well and season with salt and pepper.
3: Mix flour, cornstarch, and baking powder, along with the seasonings together.
4: Place the dry mixture in the freezer until cold.
5: Lightly dust cod filets with the flour mixture.
6: Add beer to the dry mixture to make a batter.
7: Dip the fish one at a time into the batter.
8: Drain the battered fish on a wire rack for a few minutes.
9: Heat oil to 375° and fry fish for about 3-4 minutes or until golden brown.
10: Remove fish from oil and let it cool on a wire rack.
11: Optionally, place in a preheated oven at 250 degrees to keep warm while cooking the rest of the fish.
12: For tartar sauce, mix all ingredients together and refrigerate for at least one hour before serving.
