Name: Potato-Kasha Knishes
Cook time: P0Y0M0DT1H0M0.000S
Total time: P0Y0M0DT2H30M0.000S
Yield: 6 knishes
Cuisine: jewish-cooking
Ingredients: 1 1/2 cups all-purpose flour, plus more for dusting; 3 tablespoons extra-virgin olive oil, plus more for brushing; Kosher salt; 1/4 cup plus 2 tablespoons cold seltzer; 2 teaspoons apple cider vinegar; 1 1/2 pounds russet potatoes, peeled and quartered; Kosher salt; 4 tablespoons extra-virgin olive oil; 1 1/2 pounds Spanish onions, diced; 1 clove garlic, smashed; 1 cup whole or coarse kasha (roasted buckwheat groats; available in the bulk aisle or near the dried beans); Freshly ground pepper; Spicy mustard, for serving

Directions

Make the dough: Put the flour in a food processor, then pulse as you pour the olive oil through the feed tube. Scrape down the sides of the processor and pulse again.
Dissolve 1 teaspoon salt in the seltzer and vinegar in a liquid measuring cup. Pulse as you pour the liquid through the feed tube, 20 to 30 seconds. Turn the dough out onto a floured surface and knead until smooth. Flatten into an even disk, wrap in plastic wrap and refrigerate at least 2 hours.
Make the filling: Put the potatoes in a saucepan, cover with water and season with salt. Simmer until tender, 20 to 30 minutes. Drain and coarsely mash in a large bowl.
Heat 2 tablespoons olive oil in a large skillet over medium-high heat. Add the onions, garlic and 1 teaspoon salt. Cover and cook about 5 minutes; uncover and cook, stirring, until browned, 15 to 20 more minutes.
Meanwhile, combine the remaining 2 tablespoons olive oil and the kasha in a small saucepan over medium-high heat and cook until toasted, about 4 minutes. Add 1 3/4 cups water and 1 teaspoon salt. Reduce the heat to medium, cover and cook until the water is absorbed, about 10 minutes. Season with salt and pepper. Cool slightly, then add to the bowl with the potatoes. Add the onions and mash.
Remove the dough from the refrigerator 30 minutes before making the knishes. Preheat the oven to 375 degrees F; lightly brush a baking sheet with olive oil.
Make the knishes: Put the dough on a floured sheet of parchment paper; dust with flour. Stretch into a 6-by-8-inch rectangle, then use a rolling pin to roll into a 12-by-18-inch rectangle. With the long side of the dough in front of you, shape the filling into a tight log, leaving a 2-inch border on the side closest to you and 1 1/2 inches on each end. Use the parchment paper to help roll the dough around the filling, stretching the dough as needed to keep it tight. Brush off the flour as you roll. Pinch the dough closed at the seam, then carefully turn the roll seam-side down on the parchment paper. Pull on the ends of the dough and twist to seal; pinch off the excess dough. Press the handle of a wooden spoon into the log to divide it into 3 even sections. Seal each piece closed by stretching the dough over the open sides; twist the dough and pinch off any excess. Cut each piece in half with a sharp knife to make 6 knishes. They should be closed on one side. With the cut side up, stretch the dough partly over the filling, leaving some exposed. Flatten each knish slightly so it is about 1 1/2 inches high.
Place the knishes 2 inches apart on the baking sheet. Bake 30 minutes; brush with olive oil and continue baking until golden, 25 to 35 more minutes. Serve with mustard.