- Heat oil to 350°F in a deep fryer or a medium-sized saucepan. 
- Make sure it's hot enough to crisp up the fish nicely. 
- In a mixing bowl, combine the flour, cornstarch, baking powder, salt, and cayenne pepper. 
- Stir until well mixed. 
- Pour the cold beer into the dry ingredients slowly. 
- Whisk until you have a smooth batter, and it's key to keep the beer cold for a light batter. 
- Dip each fish fillet into the batter, ensuring it is completely coated. 
- Lift and let any excess batter drip off. 
- Carefully place the coated fish into the hot oil. 
- Fry them in batches until golden brown, usually about 4-5 minutes per side.