Crispy Battered Cod with Creamy Hoisin Tartar Sauce

Name: Crispy Battered Cod with Creamy Hoisin Tartar Sauce
Ingredients: ¾ cup mayonnaise; ⅓ cup finely chopped dill pickles; 1 Tbsp. finely chopped cilantro; 1 Tbsp. hoisin sauce; 1 Tbsp. grated onion; 1 tsp. fish sauce; ½ tsp. kosher salt; Pinch ground white pepper; ½ cup all-purpose flour; ¼ cup rice flour; ¼ cup yellow corn flour; 1 tsp. baking powder; 1 tsp. five-spice powder; 1 tsp. kosher salt; 1 tsp. sugar; 1 cup cold club soda or seltzer; ¼ cup cornstarch; Vegetable oil, for frying; 1½–2 lb. cod fillets, divided into 4 pieces total; Flaky sea salt and ground white pepper; Coarsely chopped cilantro, for garnish; 1 small red chile, very thinly sliced (optional)