Knishes can be stuffed with a wide variety of fillings, including sauerkraut, kasha, and cheese, but potato and onion—preferably cooked in schmaltz—is one of the most popular fillings.

Prepare the dough for:

While the dough rests, prepare the filling. Peel and quarter:

Place in a large pot and cover with cool water. Bring to a boil over high heat, then reduce the heat to maintain a gentle simmer. Simmer until the potatoes are tender, 15 to 20 minutes.

While the potatoes cook, heat in a large skillet over medium heat:

Add and cook, stirring, until softened and starting to brown, about 15 minutes:

When the potatoes are tender, drain well. Rice or mash the potatoes until smooth and stir in the cooked onions. Add:

Preheat the oven to 375°F. Lightly oil a large baking sheet.

Divide the dough in half. Roll and stretch out one piece of dough very thin, into a roughly 12-inch square. You should not need to use any flour during the rolling process. In fact, you want the dough to stick a little to the surface to help stretch it thin enough. Place half the potato filling in a 3-inch-wide mound along the bottom edge of the dough, leaving 1 inch of bare dough on the right and left sides and about 2 inches of bare dough along the bottom edge. Roll up the dough loosely like a jelly roll. Use the side of your hand, like a karate chop motion, to press the filling down every 3 inches, then use a knife to cut through the dough in those places. Seal one side of each knish, then turn so the seam is on the bottom. Close the top of the knishes as best as you can and squish them gently to make the sides bulge out a bit, giving them a plump shape. Place on the prepared baking sheet. Repeat with the remaining dough and filling.

Brush the knishes with:

Bake until golden brown, about 40 minutes. Serve warm or at room temperature with: