Cook the Potatoes First, we cook the potatoes. Use a vegetable peeler to take off all of the skin. Be sure to put the tip of the peeler into the potato to remove any deep parts. Next, cut the potatoes into large chunks, which will help them cook faster. Place the potatoes into a pot of boiling water. Cook for around 15-20 minutes, until they are soft. Now, drain the pot into a colander. Mash the Potatoes Put the potatoes back into the pot and then mash them well. Measure out 1 cup of mashed potatoes. This is going to be for the dough. Put the measured potatoes into a bowl. Add the oil and salt, then mix it together. You’ll see it gets nice and creamy. Prepare the Flour Mixture In a separate bowl, add the baking powder to the flour. Whisk them together. Add about one-third of the flour mixture to the mashed potatoes and mix. In sections, add in all the flour as best you can. Knead the Dough Next, make a small well in the center of the bowl. Pour the cold water right into that spot. Knead the dough with your hands for a few minutes. The dough will come together, and soon you have a nice, firm ball. Place a wet cloth or towel on top of the dough, and let it sit for 30 minutes. Combine the Ingredients Meanwhile, cut and peel the onion. Dice it into small pieces. Then melt the butter in a pan to medium high heat. Add the onions and sauté until they are soft, but not yet brown. Pour the onions into a mixing bowl. This will be for our knish filling. Add 1½ cups of mashed potatoes, ½ teaspoon of salt, and ¼ teaspoon of pepper. Combine everything together. Preheat the oven to 425 degrees. Roll the Dough Flour a flat surface and a rolling pin. Place down the dough, and divide it into four parts. Take one part and prepare it for rolling. Roll out the dough, flipping it over occasionally, so it is one-quarter of an inch thick. Make a Square Knish For a square knish, with a pizza cutter or knife, trim the edges of all sides of the dough so it forms a rectangle. Place the potato filling into the center of the square. Fold over the short sides and push down on the edge. Next, fold over the longer sides. You’ll see how the dough forms a pocket around the filling. Dip your fingers into some water, then wet the dough to help seal the edges. Place the knish on a baking sheet lined with parchment paper. Crack an egg, and beat it with a fork. Paint the egg on the knish with a brush for the final touch. Make a Round Knish To a make a round knish, use a bowl to help make an even circle with the rolled dough. Place the filling in the center, pull up the sides, and pinch the dough at the top. Place it on the baking sheet, and brush with the egg. You could also make a long knish log or cut the log into small bite-sized knishes. Bake the Potato Knishes Place the pan into the oven, and cook for about 20-25 minutes. You can see how the egg brings a nice golden color to the finished knishes. Enjoy the knishes as a side dish or a snack.