How to cook
If the fish fillets you're using have skin, carefully remove it. Also clean it from any bones, if there are any. Wash, dry, cut it into pieces and lightly salt it.
In a bowl, beat the eggs with a little salt. Add the lemon juice and beer. Add the flour and baking powder in portions, while beating with a wire whisk until the mixture turns smooth and thick.
Figure out how much flour to add. When you dip the piece of fish, the breading should stick, not drip off of the fish. Yes, it will drip off a little anyway, but that's normal.
Heat plenty of oil over high heat. Fry at the last degree below the maximum.
Dip each piece of fish in the breading and immediately put it in the hot oil. Fry until it's golden brown on both sides.
A golden crisp is achieved very quickly given the temperature and you may worry that the inside of your fish may remain raw. Don't worry about it because it won't. White fish cooks very quickly and when you take it out of the hot oil, it will continue to cook because it is surrounded by the still hot breading.
It becomes a very tender and pleasant breaded fish, even if the pieces are thicker, they will not remain raw.