Preheat oven to 450 degrees. Arrange racks in upper and lower thirds of oven.
Cut potatoes lengthwise into 1/4-inch thick strips. Rinse well in a large bowl of cold water, and pat dry with a kitchen towel. Transfer to a large baking sheet. Drizzle with 1 tablespoon oil, and sprinkle with 1/4 teaspoon each salt and pepper; toss well. Arrange strips in an even layer on the sheet. Bake on lower rack until golden and crisp, about 30 minutes.
Meanwhile, place fish fillets in a large bowl. Add buttermilk, and gently turn fish to coat. In another shallow bowl, combine cornmeal, paprika, and remaining 1/4 teaspoon salt and pepper. Add fillets to cornmeal one at a time, turning to completely coat. Transfer to a plate while repeating with remaining fillets.
Heat a 12-inch cast-iron skillet over medium-high heat. Add remaining tablespoon of oil; swirl to coat. Add fillets, being careful not to overcrowd pan. Cook until nicely crusted, about 1 minute; turn over with a spatula. Place skillet in top third of oven, and cook until firm but beginning to flake when pressed in the center, about 8 minutes. Transfer to plates, and serve with potatoes. Serve lemon wedges and malt vinegar on the side.