Beer Battered Fish

Name: Beer Battered Fish
Ingredients: 1 1/2 c. cornstarch, divided; 4 tsp. kosher salt, divided, plus more for sprinkling; 2 tsp. ground black pepper, divided; 1 c. all-purpose flour; 1 tsp. baking powder; 1 tsp. paprika; 1 (12-oz.) bottle lager beer, cold; Vegetable oil, for frying; 3 lb. 1-in. thick skinless cod filets; Lemon wedges, for serving; Malt vinegar, for serving; 1 c. mayonnaise; 1/3 c. dill pickle relish; 1 tsp. lemon zest; 2 tbsp. lemon juice; 1 tbsp. chopped fresh dill; 1/4 tsp. kosher salt; 1/4 tsp. ground black pepper