Knish with Potato Filling

Ingredients:

Directions:

1. Whisk flour, salt, and baking powder together in a bowl. Make a well in the center. Add the beaten egg, white vinegar, canola oil, chicken fat, and warm water. Mix by hand until dough forms. Turn dough out onto a lightly floured surface and knead until soft and smooth. Wrap in plastic wrap and set aside.
2. Place the potatoes in a large pot with 1 tablespoon of kosher salt and enough water to cover the potatoes by 1-inch. Bring to a boil, then reduce heat to low and cook for 10 minutes. Drain the potatoes in a colander, then transfer to a large mixing bowl. Add in the sour cream, shredded cheese, and pinch of salt and pepper, and mash.
3. Melt butter in a skillet over medium heat. Add onion, chicken fat, and kosher salt, cook and stir for 10 minutes. Transfer mixture to the mashed potato bowl. Season with salt and pepper. Mash until combined. Set aside to cool.
4. Preheat the oven to 375° F. Line two baking sheets with parchment paper.
5. Divide dough in half; flatten one half into a rectangle on a lightly floured surface. Roll out into a larger rectangle about 1/8-inch thick, pulling the corners as needed.
6. Place half of the filling over one long end, about 3 inches away from the edges. Beat egg with water and brush over the opposite end and a little on the sides. Stretch the dough to cover the filling, then roll up toward the egg-washed side. Fold the last 3 or 4 inches over the top, then press in the seam to seal roll over so seam-side is on the bottom. Trim off any excess dough from the ends.
7. Gently mark the dough into 8 equal pieces with a spatula, pressing down but not cutting. Flour the side of your hand and press into the marks. Rub back and forth to separate each piece. Position each piece with one cut end facing down and the other facing up. Squish down the top and press everything into the center to form a round knish.
8. Repeat with remaining dough and filling.
9. Brush bottoms of each knish with olive oil and place on the baking sheets. Brush the tops with any remaining egg wash.
10. Bake for about 40 minutes, until lightly golden-brown.
11. Remove from the oven and let cool for a few minutes before serving.