Prepare the batter by sifting the flour and rice flour into a large mixing bowl.
Add the baking powder, sugar, salt, and black pepper into the bowl and mix well.
In a separate bowl, combine the lager beer and soda water.
Gradually add the wet mixture to the dry ingredients while whisking until the batter is smooth, then let it rest for 30 minutes.
Peel and cut the potatoes into thick chips.
Blanch the chips in hot oil at 320°F until they are just tender, then remove and drain on paper towels.
Increase the oil temperature to 375°F and fry the chips again in batches until golden and crispy, about 7-8 minutes.
Season the chips with sea salt and set them aside.
Heat the oil in a deep fryer to 350°F (175°C).
Coat the cod fillets in a little flour, then dip them into the batter, ensuring they are fully coated.
Carefully place the battered fish into the hot oil, frying them for 3-3 1/2 minutes, basting with oil on each side until golden and crispy.
Remove the fish from the oil and drain on a wire rack.