For fries, heat oil to 320° in a heavy skillet or pot on medium high heat (oil will shimmer and a drop of water will sizzle when ready). Add potatoes and fry 2 min or until soft/limp. Remove from oil and drain well, cooling to room temp. Raise oil temp to 375° and fry potatoes until crispy, approx. 3 min. Remove fries and toss with salt and pinch of pepper. Set aside to keep warm.
Dredge fish pieces in cornstarch to coat well. Combine flour, baking powder, salt, pepper and beer. Immediately dip fish into batter, then carefully drop in hot oil (350°). Cook 3-4 min, turning a few times, until golden and fish flakes easily. Serve immediately.