Beer-battered Cod and Onion Rings

These fried fish and onion rings, covered with homemade beer batter, are crunchy and ridiculously addictive.
Whisk together the flour, baking powder, 1/2 tsp salt, pepper, egg, and beer in a large bowl.Preheat the oven to 200 degrees. In a 6-to 8-cc saucepan, heat 2 inches of oil to 375 degrees over medium-high heat. Add the onion to the batter, turn it over so that it is well coated, then put a few onion rings in the mold (not too many). Cook, turning frequently, until golden brown, about 6 minutes. Transfer to a wire rack set on a baking sheet, sprinkle with salt and place in the oven to preserve the heat. Repeat with the remaining onion.Allow the oil to heat to 375 degrees and remove the foam to remove any dough pieces. Add the fish to the batter and turn it over to coat well. Saute the fish in the preheated oil, turning and pressing as needed, until dark golden brown, about 7 minutes. Place on a wire rack and sprinkle with salt.Add the lemon slices and parsley to the butter and cook until crisp, about 1 minute.Place the fish and onion rings on a platter and garnish with sauteed lemon slices and parsley.Note: A nutritional analysis is provided for each serving.