Gather the ingredients so you have everything close at hand on the counter or table.
Prepare the Fish
On a cutting board, slice fish into desired lengths. If I am deep frying the fish (for fish tacos), I will cut fish into 2-3" pieces. However, if I'm frying the fish in a cast iron skillet, I will use bigger pieces.
Place the fish in a shallow bowl. Pour dark ale beer over fish and allow to soak for 30-60 minutes before cooking.
Make the Tarter Sauce
While the fish is soaking, prepare the homemade tarter sauce. Spoon salad dressing in a small serving bowl.
Stir in sweet relish until combined.
(If you prefer a tarter sauce that is less sweet, you may substitute real mayonnaise for the salad dressing, and a dill relish in place of sweet.)
Fry the Fish
Using a gallon bag, combine cornmeal, all-purpose flour, and Cajun spice. Mix well. Place pieces of strained fish into the flour. Toss until fish is well coated.
Preheat enough oil in a cast iron skillet or Dutch oven for frying, between 1-4 inches.
When oil has reached the proper temperature (375 degrees), add 10-12 pieces of fish at a time, being careful not to overcrowd. Cook for 3-4 minutes until a deep golden brown on both sides.
Remove fish with a spatula or wire strainer and place on paper towels to soak up excess oil. Sprinkle fish with salt and pepper as desired.
If needed, return oil to cooking temperature and repeat until all of the fish has been fried. Serves 4-6.