Add the oil to a 4- or 5-quart pot and heat it until it reaches 350°.
In the meantime. pat the cod dry on both sides with paper towels and set them on a sheet tray lined with parchment paper.
Gently season the fish on all sides with coarse salt. Set them to the side.
In a medium-sized bowl whisk together the flour, cornstarch, baking powder, granulated garlic, granulated onion, paprika, cayenne, salt, and pepper.
Take ⅔ cup of the mixture and sprinkle it on a sheet tray lined with parchment paper.
Dredge the fish in the seasoned flour on the sheet tray until coated on all sides, and then set them to the side on the tray. They can sit like this for up to 10 minutes.
While it is sitting in the flour you can make the tartar sauce and shred the cabbage. Set them to the side.
Next, whisk the beer into the bowl of seasoned flour until it is thoroughly combined. It is like the consistency of a pancake batter. Be sure to watch my video.
Shake off any excess flour from the fish and then add it to the beer batter and submerge it completely.
Give the fish a little shake and then slowly add it to the oil while slowly waving it back and forth for 10 to 15 seconds so that it begins to fry to prevent it from sticking to the bottom of the pot.
Cook for 5 to 7 minutes or until golden brown on the outside and cooked throughout.
Set the fish to the side on a rack over a sheet tray to drain off any excess oil. Repeat the process until all the fish is fried.
Add some shredded cabbage to the bottom of the toasted bun.
Place on a piece of fried fish and add the tartar sauce and top bun. Make the other fish sandwiches and serve.
