Prep the potatoes: Cut the russets into even fries.
Soak in cold water for 20–30 minutes to remove excess starch. Drain and pat very dry.
Par-cook the fries: Toss dried fries with 1 tablespoon oil and a pinch of salt. Air fry at 360°F (182°C) for 12–15 minutes, shaking halfway, until tender but not fully browned.
Set aside.
Preheat the air fryer: Increase temperature to 400°F (204°C). Let it heat while you batter the fish. A hot basket helps prevent sticking.
Make the batter: In a bowl, whisk 1 cup flour, cornstarch, baking powder, garlic powder, paprika, 1/2 teaspoon salt, and a few grinds of pepper.
Whisk in cold beer (and egg if using) until smooth. The batter should be the consistency of heavy cream. If too thick, add a splash more beer; if too thin, add 1–2 tablespoons flour.
Prep the fish: Pat fillets dry.
Season lightly with salt and pepper. Place 1/2 cup flour in a shallow dish for dredging.
Coat the fish: Working one piece at a time, dredge fish in flour, shake off excess, then dip in batter. Let excess drip for 2–3 seconds.
This helps a thin, even coat form.
Air fry the fish: Lightly spray the air fryer basket. Place battered fish in a single layer with space between pieces. Lightly mist the tops with oil spray.
Cook at 400°F (204°C) for 8–10 minutes, flipping carefully at 5–6 minutes and misting again. Fish is done when coating is deep golden and flakes easily.
Finish the fries: While the fish rests 2 minutes, return par-cooked fries to the basket. Air fry at 400°F (204°C) for 6–8 minutes until crisp and browned, shaking once.
Season with salt while hot.
Serve: Plate fish and chips with lemon wedges, malt vinegar, and tartar sauce. Eat right away for peak crunch.