Start the batter: Whisk self-rising flour, rice flour, and baking powder together in a bowl. Freeze until ready to use.

Make the fish: Pat cod as dry as possible, then cut lengthwise into eight 1-inch-thick strips. Place rice flour on a plate and season with salt. Dust cod lightly with the rice flour mixture and shake off any excess. Cover a plate with crinkled foil to make a quick drying rack; place cod on top.

Heat oil in a deep-fryer to 375 degrees F (190 degrees C).

Finish the batter: Remove flour mixture from the freezer. Pour in beer and whisk until batter is the consistency of a thick pancake batter, adding more beer as needed.

Dip floured cod into the batter to coat; lift out and let excess drip off.

Fry cod in batches until golden brown, dunking occasionally if needed, 3 to 4 minutes. Drain on paper towels. Serve immediately.