Grandpa's Beer Battered Fish

1 gallon vegetable, or canola, oil
2 cups flour
1 tablespoon baking powder
1 teaspoon kosher salt
¼ teaspoon cayenne pepper
Dash Old Bay Seasoning
1 bottle brown beer, cold
1½ pounds firm-fleshed whitefish (tilapia, pollock, cod), cut into 1-ounce strips
Cornstarch, for dredging
Malt vinegar, for serving

Heat oven to 200F.
Heat the oil in a 5-quart Dutch oven over high heat until it reaches 350 degrees.
In a bowl, whisk together the flour, baking powder, salt, cayenne pepper, and Old Bay seasoning. Whisk in the beer until the batter is completely smooth and free of any lumps. Refrigerate for 15 minutes. Note: The batter can be made up to 1 hour ahead of time.
Lightly dredge fish strips in cornstarch. Working in small batches, dip the fish into the batter and immerse in the hot oil. When the batter is set, turn the pieces of fish over and cook until golden brown, about 2 minutes. Drain the fish on a wire rack set over a baking sheet. Keep the fried fish in the warmed oven while you cook the remaining batches. Serve with malt vinegar.