Cut the potatoes into thick steak fries. Submerge in a large bowl of water as you heat the oil.
Heat the oil in a large Dutch oven or wok to 285°F; use an instant-read thermometer for accuracy.
Drain the potatoes and spread out on plenty of paper towels; blot with more paper towels. Place in a large mixing bowl and sprinkle over the cornstarch, onion powder, and 1 teaspoon salt; toss to combine.
Working in two batches, deep-fry the chips until soft and starting to color, about 10 minutes. Drain on paper towels and loosely cover with aluminum foil to keep warm.
Increase the temperature of the oil to 355°F. Working in two batches, return the chips to the oil and fry until golden brown and crisp all over, about 5 minutes.
Remove from the oil and drain on paper towels. Season with salt and loosely cover with aluminum foil to keep warm; reserve the oil.
Return the frying oil to 355°F.
While the oil heats up, season the fish fillets with salt and pepper. Place the cornstarch in a bowl and season with a little salt and pepper.
Combine the flour, egg, 1 teaspoon salt, and 1/2 teaspoon black pepper in a large mixing bowl; whisk to combine. Slowly whisk in enough of the beer to make a thick, smooth batter.
Working in batches of two, add the fish fillets to the cornstarch and turn to coat. Shake off any excess before dropping into the batter, turning to coat evenly.
Let the excess batter drip off before carefully lowering into the hot oil. Deep-fry until golden brown and crisp, carefully turning as needed, about 4 minutes. Remove from the hot oil and drain on paper towels; loosely cover with foil to keep warm. Repeat steps 10 & 11 for the remaining fish.
If needed, after cooking the fish, reheat the chips in the hot oil. Drain and season with salt.
