1. In a large bowl, mix both flours, baking soda and sugar.
2. Add soda water, beer and salt.
3. Mix only until the batter binds together and is smooth. Be careful not to over-mix.
4. Cover your fish with a dusting of plain flour, then drop into the batter and coat completely.
5. Pre-heat vegetable oil in deep fryer (or place about 1 1/2 inches in a wide, deep pot on stove top) to 375 F (190 C) on a deep fry thermometer.
6. Once fish is coated with batter, gently place into the 375 F oil and cook until underside of fish is golden brown, about 1-2 minutes. Turn and brown other side a minute or two. Lift from oil, drain on paper towels and serve with tartar sauce. Cook fish in batches to maintain oil temperature.
7. For Tartar Sauce: Add all tartar ingredients together and mix. Add salt to taste and hot sauce if you want heat. Can be made a 1-2 days ahead and stored in the refrigerator.
FRYING NOTES: For perfectly browned and cooked fish, make sure the oil remains at 375 F before dropping in the fish. When you drop in each fish portion, the oil cools down, so in between batches bring the oil temp back to 375 F. Do not overcrowd the fryer. Each portion needs to have enough oil surrounding it to make sure it cooks evenly. Otherwise, you’ll end up with a sloppy, oily piece of fish!