Preheat oven to 200F.

Toss shrimp or fish with vinegar.

Combine salt, pepper, turmeric, curry powder, and cayenne (if using).

Rub the spice mixture into the fish or shrimp.

Heat oil in a large nonstick skillet over medium-high heat (1/8 inch depth).

Mix flour with warm water to create a yogurt-like paste.

Dip each piece of shrimp or fish into the batter.

Fry in hot oil, raising heat to high, rotating to brown evenly, for 5-8 minutes until golden and crisp.

Cook in batches to avoid crowding.

Keep cooked pieces warm in the oven.

Serve with lime wedges and cilantro garnish.

For a spicier version, proceed with the following steps:

Quickly brown the shrimp or fish, about 2 minutes per side.

Remove the shrimp or fish to a plate.

Pour out most of the oil, leaving 2 tablespoons.

Add sliced onions, curry powder or garam masala, and minced chiles to the skillet.

Cook over medium-high heat, stirring occasionally, until onions are wilted and browned (at least 10 minutes).

Add water, bring to a boil, and return the fish or shrimp to the skillet.

Simmer until fish is cooked through, about 5 minutes.

Serve over white rice.