Heat the avocado oil over medium to medium high heat in a dutch oven or large cast iron skillet.
Prepare a small bowl of 1/2 cup flour, 1 tsp old bay seasoning, 1/4 tsp sea salt, and 1/4 tsp black pepper.
In a separate large mixing bowl, combine:1 cup Flour1 tbsp Old Bay Seasoning1/4 tsp Sea salt1/4 tsp Black pepper1/2 tsp Baking powder1 Egg1 cup Lager beer
Once the oil is hot (around 375℉), pat the cod filets dry, lightly flour with the first flour mixture, and dredge the cod in the beer batter.
Gently place the battered fish into the hot oil.
Fry for 4-5 minutes, flip, and fry the second side for another 4-5 minutes.
Once cooked through and golden brown, remove to a paper towel lined plate.
Assemble the sandwich by spreading tartar sauce on the bottom bun, next the lettuce, beer battered cod, cheddar cheese and top bun.