Add dry ingredients to a bowl. Add beer and whisk to ensure no lumps. Cover and refrigerate 20-30 minutes.
As you wait for the batter to firm up, add oil to an electronic fryer or a deep Dutch oven (you may need to add more oil if you have a wide pan so there’s enough to coat the fish). Bring oil up to 375 degrees and test with a deep fry thermometer.
When oil reaches 375, remove fish from the refrigerator, pat the pieces dry with paper towel; sprinkle with a little kosher salt and black pepper.
Remove batter from the refrigerator and stir to refresh.
Set up a rack over a baking tray, or place paper towels or a newspaper on a plate - this will be for draining the cooked fish.
Drop 2-3 pieces of fish into the batter to coat well.
Lightly pick up each piece with a fork and carefully place it into the hot oil, going away from you, to avoid splattering.
Cook 2-3 pieces at a time, depending on size of pan and the thickness of your fish (and you don’t want to crowd the pieces or they’ll stick to each other). The fish should take 3-4 minutes or until golden brown. Remove with tongs or slotted spoon, place on draining area and sprinkle each with a bit of kosher salt.
Test oil to ensure it’s 375 degrees, then repeat process for remaining fish. Optional - squeeze on a little lemon juice. Serve with Mango/Cilantro Sauce.