Preparation Pour enough oil into heavy large skillet to reach depth of 1/2 inch. Heat oil over high heat until thermometer registers 360°F. Meanwhile, whisk flour and 1/2 cup water in medium bowl until smooth batter forms. Sprinkle fish with salt and pepper. Add fish to batter and stir to coat. Add potato to skillet; fry until golden brown and crisp, stirring often, about 7 minutes. Using tongs, transfer potato to paper towels. Sprinkle with salt and pepper. Add fish to skillet; fry until coating is golden and crisp and fish is just opaque in center, about 3 minutes per side. Transfer fish to paper towels. Sprinkle with salt and pepper. Serve with vinegar.
Preparation Pour enough oil into heavy large skillet to reach depth of 1/2 inch. Heat oil over high heat until thermometer registers 360°F. Meanwhile, whisk flour and 1/2 cup water in medium bowl until smooth batter forms. Sprinkle fish with salt and pepper. Add fish to batter and stir to coat. Add potato to skillet; fry until golden brown and crisp, stirring often, about 7 minutes. Using tongs, transfer potato to paper towels. Sprinkle with salt and pepper. Add fish to skillet; fry until coating is golden and crisp and fish is just opaque in center, about 3 minutes per side. Transfer fish to paper towels. Sprinkle with salt and pepper. Serve with vinegar.