1. Slice each filet into 4 pieces, set aside. Get your oil going: You want it to be 350-360 degrees. Turn the oven to 200 degrees, put a cookie sheet inside. Place a wire rack on top of the cookie sheet.
2. Mix the flour, vegetable oil, salt, baking powder and beer together, stirring all the while. You want enough beer in the batter to give it the consistency of house paint, or melted ice cream. Put in the fridge to rest for 20 minutes.
3. While the batter is resting, cut potatoes into 1/2" wide fries and put them into a large bowl of cold water. When you are done, remove and pat them dry with a paper towel.
4. Fry the potatoes, a few at time, until they just before browning. Lay on paper towel to remove grease, then remove paper towel and place on pan in the oven.
5. Take the batter out of the fridge. Dredge the fish in the batter and let the excess drip off for a second or two. Lay each piece gently into the hot oil. Do this by letting the bottom end of the piece of fish fry for a second or so in the oil before you let the whole piece get a bath. This helps prevent the fish from sticking to the bottom of the pot. Keep a chopstick or something similar around to dislodge any pieces that do get stuck. Fry in batches until golden brown, about 4 minutes depending on how large the pieces are. Keep each batch in the warm oven while you finish the rest.
6. Place potatoes back in oil & fry til golden brown. Place on paper towel. Salt each batch the moment it comes out of the fryer. Store each batch on the wire rack in the oven.