This recipe comes from the Low fat Vegetarian Jewish Cookbook. These are probably the best Knishes I've ever made. I make mine round but you can make them square also. I serve them with Vegan sour cream or Dijon Mustard.
Peel and chop the potatoes. Put them in the cold water then cook them in a covered pot for 20 minutes. Drain.
Heat the sauerkraut and caraway seeds in 1/8 cup of water in a small pot over medium heat for 5 minutes.
Mash cooked potatoes and divide mixture into thirds. Stir 1/3 of the mashed potatoes with sauerkraut mixture. Mix remaining mashed potatoes with turmeric, salt, flour and baking powder to create a dough.
Knead the dough for a few minutes. Then roll dough out onto a floured surface until 1/4 inch thick.
Cut the dough into 4"x4" squares (about 8). Place 1/8 of the filling on each square. Fold corners of the dough in and pinch dough tight in the center.
Preheat your oven to 375'F. Place knishes pinched side down on a lightly oiled baking sheet. Bake for 45 minutes. Serve warm with a dollop of sour cream.