Red Potato Knish with Kale, Leeks and Cream Cheese

Make Dough

Stir together your dry ingredients in the bottom of a medium/large bowl. In a small bowl, whisk together the egg, oil, vinegar and water. Pour it over the dry ingredients and stir them to combine. Once the mixture is a craggy, uneven mass, knead it until smooth, about a minute. Place the dough back in the bowl and cover it with plastic wrap. Set it aside for an hour (or in the fridge, up to 3 days) until needed.

Prepare Filling

Put potatoes into a large pot, cover with cold water, and bring to a boil over high heat. Reduce heat to medium and cook until soft, about 20 to 25 minutes. Drain, then transfer to a large bowl to cool. Fill a medium bowl with very cold water and drop in leek rings. Swish them around with your fingers, letting any sandy dirt fall to the bottom. Scoop out the leeks and drain them briefly on a towel, but no need to get them fully dry. Do the same with the kale, but you can leave the leaves to nearly fully dry, patting them if necessary, on the towels while you cook the leeks. Heat a large, heavy skillet over medium heat. Once hot, add butter and oil and once they're fully melted and a bit sizzly, add the leek slices. Reduce heat to low, cover with a lid and cook leek for 20 minutes, stirring occasionally. Raise heat back to medium, add the kale ribbons and cook until they wilt, about 5 minutes. Transfer mixture to bowl with potatoes, add the cream cheese and mash together until combined. Stir in salt and many grinds of black pepper and set filling aside.

Assembly Part 1

Line a large baking sheet with parchment paper and preheat your oven to 375 degrees. If your dough has sweated some beads of oil while it rested, fear not, you can just knead it back into an even mass. Divide the dough in half. On a well-floured surface, roll the first half of the dough into a very thin sheet, roughly in the shape of a 1-foot square, but really, no need to be rigid about it. For moderate size knish (smaller than the traditional "doorstops" but still hefty, about 3 inches across), create a 2-inch thick log from half your potato filling across the bottom of your dough. Roll the filling up in the dough like you were rolling a cigarette, but not too tight. A tiny amount of slack will keep the dough from opening in the oven. Keep rolling until the log has been wrapped twice in dough. Trim any unrolled length and add it to the second half of the dough; it can be used again. Repeat the process with the second half of your dough and second half of filling; you might have a small amount of dough leftover.

Assembly Part 2

Trim the ends of the dough so that they're even with the potato filling. Then, make indentations on the log every 3 to 3 1/2 inches (you'll have about 3, if your log was 1 foot long) and twist the dough at these points, as if you were making sausage links. Snip the dough at each twist, then pinch one of the ends of each segment together to form a sealed knish base. Use the palm of your hand to flatten the knish a bit into a squat shape and from here, you can take one of two approaches to the top: You can pinch together the tops as you did the bottom to seal them; indenting them with a small dimple will help keep them from opening in the oven. You can gently press the dough over the filling but leave it mostly open.

Bake Knish

Arrange knish on prepared baking sheet so that they don't touch. Whisk egg yolk and water together to form a glaze and brush it over the knish dough. Bake knish for about 45 minutes, rotating your tray if needed for them to bake into an even golden brown color. Let them cool a little bit before digging in. Spicy mustard is a traditional accompaniment, but you can use a dollop of sour cream too.