Coney Island Knishes

To make the dough: Whisk flour, kosher salt, and baking powder together in a large bowl. Make a well in the center. Add oil, warm water, beaten egg, and vinegar. Mix by hand until dough pulls together. Turn dough out onto the counter and knead until soft, smooth, and elastic. Wrap in plastic wrap and refrigerate for at least 1 hour.

Meanwhile, to make the filling: Place potatoes into a large pot and cover with salted water; bring to a boil. Reduce heat to medium-low and simmer until tender, about 20 minutes. Drain, then transfer to a mixing bowl. Mash and set aside.

Chop corned beef and cabbage into fine pieces.

Melt butter in a large skillet over medium heat. Add onion, corned beef, cabbage, and kosher salt. Cook and stir until onions are soft and golden brown and beef fat is rendered, about 10 minutes.

Transfer beef mixture to the bowl with mashed potatoes. Season with cayenne pepper, salt, and black pepper. Mix until combined, then let filling cool to room temperature.

Preheat the oven to 375 degrees F (190 degrees C). Line 2 baking sheets with silicone mats.

Divide chilled dough in half; flatten one half into a rectangle on a floured surface. Roll out into a larger rectangle about 1/8-inch thick, pulling the corners as needed.

Place 3 cups filling over one long end, about 3 inches away from the edges. Beat egg with water in a small bowl and brush egg wash over the opposite end and a little on the sides. Stretch dough to cover filling, then roll up toward the egg-washed side. Fold the last 3 or 4 inches on top. Press in filling; roll over so seam-side is on the bottom.

Trim off excess dough from the ends if desired. Mark, but do not cut, dough into 8 equal pieces. Flour the side of your hand and press into the marks. Rub back and forth against the counter to separate each piece. Position each piece with one cut-end facing down and the other facing up. Squish down the top and tuck everything into the center to form a round knish.

Repeat with remaining dough and filling. Brush bottoms with olive oil and place on the prepared baking sheets. Brush leftover egg wash on top.

Bake in the preheated oven until lightly golden brown, about 40 minutes. Let cool until just warm or room temperature.