Vegetable oil, for frying
4 large russet potatoes
One 12-ounce bottle of beer (preferably ale)
2 cups all-purpose flour
3 pounds cod or haddock filllets, cut into 1-inch strips
Salt and freshly ground pepper
1 teaspoon chili powder
1/2 teaspoon Old Bay Seasoning
1. Preheat the oven to 200°. Line a baking sheet with parchment paper and place in the oven. In a deep fryer or a deep pot fitted with a candy thermometer, heat 3 to 4 inches of oil to 325°. Peel the potatoes and cut into 1/2-inch-thick sticks, placing them in a large bowl of cold water as you work. Soak for 5 minutes, drain and pat dry. Fry the potatoes in 3 or 4 batches until slightly golden at the edges, about 3 minutes per batch (allow the oil to return to 325° between batches). Transfer the partially cooked potatoes to paper towels and let cool while you prepare the fish.
2. Heat the frying oil to 375°. In a medium bowl, whisk the beer into 1 1/2 cups of the flour until smooth. Season the fish with salt and pepper. Place the remaining 1/2 cup of flour on a plate. Dredge the fish in the flour, shake off any excess flour, then dip in the beer batter. Slowly lower the battered fish into the hot oil and fry, a few pieces at a time, until golden brown, about 4 minutes per batch (allow the oil to return to 375° between batches). Transfer the fried fish to the prepared baking sheet in the oven and keep warm.
3. Meanwhile, stir together the chili powder, Old Bay Seasoning and 1 teaspoon of salt. With the oil at 375°, fry the potatoes a second time, in 3 or 4 batches, until crisp and golden brown, about 4 minutes per batch. Remove the fries to fresh paper towels to drain and immediately season with the spice mixture. Serve the fries with the fish and malt vinegar.