3 eggs, divided
6 tablespoons vegetable or canola oil, divided
½ cup water
1 tablespoon cider vinegar
2½ cups all-purpose flour
4 pounds russet potatoes, peeled and cubed
2 large yellow onions, diced
¼ cup chopped fresh thyme
Ground black pepper
In a large bowl, whisk together 2 eggs, 2 tablespoons of the oil, the water, vinegar and ½ teaspoon of salt. Add the flour and knead together to form a smooth dough. Divide the dough in 2 and wrap each piece tightly in plastic wrap. Refrigerate for 1 hour.
While the dough chills, prepare the filling. Place the potatoes in a medium saucepan and fill with enough water to cover by 1 inch. Bring to a boil, then reduce to a simmer. Simmer until the potatoes are tender, 12 to 15 minutes. Drain thoroughly, then transfer the potatoes to a medium bowl. Mash the potatoes until mostly smooth. Set aside.
In a medium skillet over medium-high, heat the remaining 4 tablespoons of oil. Add the onions and cook until tender and starting to brown, about 8 minutes. Stir the onions into the potatoes, along with the thyme. Season with salt and black pepper.
Heat the oven to 375 degrees. Line a baking sheet with parchment paper.
Working with one piece of dough at a time, roll and stretch each piece until it is a long strip about 6 inches wide and 16 inches long. Spoon half of the potato filling mixture down the middle of each strip of dough, using your hands to smooth the mixture into an even mound. Dip your fingers in water and moisten the edges of the dough, then wrap both sides of the dough up and over the potato filling.
Slice each piece of dough, which now should resemble filled tubes, into 8 pieces. Turn each piece onto its side and use the palm of your hand to flatten slightly. Working in batches of 8, arrange the pieces on the prepared baking sheet, leaving about 1 inch between them.
In a small bowl, beat the remaining egg with 1 tablespoon of water until foamy. Brush a bit of the egg mixture over each knish. Bake for 30 minutes, or until deep golden brown. Let cool for 10 minutes before serving.
Nutrition values per serving: 230 calories; 6 g fat (0.5 g saturated; 0 trans); 40 mg cholesterol; 38 g carbohydrate; 3 g fiber; 2 g sugar; 5 g protein; 140 mg sodium.
Alison Ladman, The Associated Press