Step 1

To make the dough, whisk together the flour and salt in the bowl of a standing mixer (or regular mixing bowl). Whisk together the egg, sour cream, and water until combined, and then pour over the flour. Stir together the liquids and the flour with a wooden spoon or spatula until a shaggy dough is formed.

Step 2

Knead the dough the mixer on low speed with the dough hook attachment until the dough is very smooth and soft, about 5 minutes. Alternatively, knead by hand against the counter for 8 minutes. If the dough seems very sticky after a few minutes of kneading, add a tablespoon of flour at a time until it starts coming together into a smooth ball. Cover and set aside to rest on the counter while you make the filling.

Step 3

To make the filling, scrub the potatoes clean and place them in a 2- or 4-quart sauce pan. Cover with an inch or two of water and set over high heat. When the water comes to a boil, reduce the heat to medium-low and simmer until the potatoes are tender when pierced by a fork, 6 to 10 minutes depending on the size of your potatoes.

Step 4

Transfer the potatoes to a mixing bowl with a slotted spoon. Remove the peels if desired (I like to leave them on!). Mash the potatoes into large chunks with a potato masher or a dinner fork. Add the sour cream and salt, and continue mashing until the potatoes are smooth. Add the sauerkraut and cheese, and stir to combine. Taste and add more salt if needed.

Step 5

Shape the filling into 1" balls (roughly the diameter of a quarter) and arrange them on a dinner plate. Pre-shaping the filling makes it easier and quicker to shape the pierogi.

Step 6

Line a baking sheet with parchment and sprinkle generously with flour. Set this near your workspace.

Step 7

Divide the pierogi dough in half, working with one half at a time and keeping the other half covered. Sprinkle your work surface with flour and roll out the pierogi dough to 1/8" thick. Stop occasionally to lift the dough and make sure it's not sticking to the work surface; use more flour as needed. If the dough shrinks back as you roll, let it sit for 5 minutes and then roll again.

Step 8

Use a 3" biscuit cutter or drinking glass to cut the dough into rounds. Gather the scraps and set them aside.

Step 9

To shape the pierogi, hold one of the rounds of dough in the palm of your hand and set a ball of filling in the middle. Fold the round in half, pinching it closed at the top and then working your way along the sides to form a half-moon shape. Make sure the edges of the dough are completely sealed. Set the pierogi on the floured baking sheet.

Step 10

Continue to shape pierogi with the remaining rounds of dough. Lay them close together on the baking sheet, but don't let them touch. Roll out the second half of the dough, and cut and shape the pierogi as described. When finished, roll the scrapes and continue to make as many pierogi as you can. You should end up with roughly 4 dozen pierogi.→ Recipe Tip! No matter what, I always seem to end up with either a few leftover balls of filling or an extra bit of dough. C'est la vie! The balls are delicious eaten as a snack, even cold from the fridge. The scraps of dough can be rolled out, sliced into spaghetti-thin strips, and then boiled just like pasta for an afternoon snack.

Step 11

At this point, the pierogi can be boiled and served right away or frozen. To freeze, place the sheet pan of pierogi in the freezer and freeze until solid. Transfer the frozen pierogi to a freezer container and freeze for up to three months. Pierogi can be cooked straight from the freezer.

Step 12

When ready to cook the pierogi, melt the butter in a large skillet over medium heat. Add the onions and cook until the onions are translucent, very soft, and beginning to brown, 8 to 10 minutes. Push the onions to the edges of the pan where they will stay warm and continue to caramelize.

Step 13

Meanwhile, bring a large pot of water to a boil. Salt generously. Working in batches, add 10 or so pierogi to the boiling water and stir to make sure they don't stick to the bottom. Cook the pierogi until all the pierogi have floated to the surface and then 1 to 2 minutes longer to make sure the filling gets hot — 8 to 10 minutes total.

Step 14

Transfer the pierogi to the pan with the onions. Turn the heat to medium-high. Cook the pierogi without moving until they are golden and crispy on the bottoms, 2 to 3 minutes. If you're cooking more batches, transfer the pierogi to a serving dish. Once all the pierogi have been boiled and crisped, scrape the onions over the pierogi and gently stir to coat the pierogi with butter and onions. Serve immediately while hot.