Combine tartar sauce ingredients in small mixing bowl. Cover and refrigerate for at least 2 hours for best flavor.
Add several inches of oil to the bottom of a large heavy-bottomed pot (my dutch oven is my preferred pot to use), and heat over MED heat until oil reaches 375°F.
Line a baking sheet with a paper towel, then add a wire cooling rack on top. Set aside, near the stove.
While the oil is heating up, add dry batter ingredients to a mixing bowl (flour, seasoned salt, black pepper, garlic powder, paprika, onion powder) and whisk to combine. Add beaten egg and slowly whisk in beer until mostly smooth, and batter resembles a pancake batter consistency.
Pat cod pieces very dry and season with ½ tsp kosher salt and ½ tsp black pepper.
Dip a cod piece into the beer batter, turning to coat very well. Add cod slice into the hot oil, carefully dropping it away from you, then repeat with another 2-3 slices. Try not to fry more than 3-4 pieces at a time, or else the pan will get overcrowded.
Cook approximately 3-5 minutes, until golden brown on one side, then gently flip pieces over and cook another 3-4 minutes on the other side, until golden brown all over. Remove to prepared wire rack.
Repeat steps 6 and 7 with any remaining fish pieces. Serve with lemon wedges, a bit of fresh parsley, and tartar sauce.
