Knish, with variations

This recipe adapted from Sydney Oland’s excellent version, with spiritual guidance from Joan Nathan’s notes on the classic, and some new ideas introduced at the end. One note: there are several possible variations for both the dough and the fillings. Dough can be made with either oil or schmaltz, making it parve or meat, and the optional fillings could also include parve, meat, or dairy options. It’s possible to make a variety of kosher/kosher-style combinations.

For the Dough:
2 1/2 cups all purpose flour
1 teaspoon baking powder
1/2 teaspoon kosher salt
1 large egg, beaten
1/2 cup vegetable oil (or schmaltz)
1 teaspoon white vinegar
1/2 cup room temperature water

For the Filling:
1 pound russet potatoes, peeled and cut into 1 inch pieces (about 3 medium)
kosher salt and freshly ground black pepper
2 tablespoons butter
1/2 cup finely sliced scallions - green and white parts (about 4 scallions)
1 egg, beaten, with a teaspoon of water
spicy brown mustard, to serve.

parsley, optional
caramelized onions, optional
pastrami or beef salami, optional
feta, sliced olives, optional

Directions:
Gently mix all of the dry dough ingredients in a medium mixing bowl. Mix the wet ingredients. Form a well in the center of the dry ingredients and pour in the wet. Gently stir them with a wooden spoon or rubber spatula. Once incorporated, with no remaining dry spots, knead the dough on a clean work surface until it’s smooth and stretchy – about 5 to 10minutes. Form the dough into a disc shape and wrap it in plastic wrap. Let it rest at room temperature for about 1 hour.

Meanwhile, peel and boil the potatoes until they are tender and can easily be broken with a fork. Gently mash the potatoes, then add the salt and pepper, and the butter. Let cool then add the scallions and egg, plus the parsley and caramelized onions, if you are using them. Mix well. 

Preheat the oven to 375F and line a baking sheet with parchment paper.

Roll out the dough thinly, forming a rectangle that is about 32 inches wide by 16 inches long. Don’t worry if there is some tearing. 

Place your filling about 2 inches from the edge closest to you and form a log of filling that runs nearly the entire width of the dough. Roll it up and continue rolling until you have reached the end of the dough. Twist the log forming segments of dough about the size of a lemon. Do your best to seal one end and leave the other open – this will become the top of the knish. Repeat this process until you have run out of dough. Apply the egg wash and bake until a deep golden brown – about 45 minutes.