Savory Sauerkraut Pierogi with Caramelized Onions

Make the dough by whisking the flour and salt together in a large bowl. Make a well in the center, add the egg, sour cream, and warm water, then stir with a fork until a shaggy dough forms.

Turn the dough onto a floured surface and knead for 5 to 7 minutes until it becomes smooth, soft, and elastic. Wrap the dough tightly in plastic wrap and let it rest at room temperature for 30 minutes to relax the gluten.

Prepare the filling by melting 2 tablespoons of butter in a skillet over medium heat. Add half of the chopped onion and all the mushrooms, sautéing for 5 minutes until soft and golden brown.

Stir in the drained sauerkraut and black pepper. Cook the mixture for 10 minutes, stirring occasionally, until all excess moisture has evaporated and the sauerkraut is slightly caramelized, then let it cool completely.

Roll out half of the rested dough on a lightly floured surface to about 1/8-inch thickness. Use a 3-inch round cookie cutter or glass rim to cut out dough circles.

Place a rounded teaspoon of the cooled filling in the center of each dough circle. Fold the dough over to form a half-moon, pinching the edges firmly together with your fingers to seal completely without trapping air.

Bring a large pot of salted water to a gentle boil. Drop the pierogi in batches of 6 to 8 into the water, cooking until they float to the surface, plus an additional 2 minutes, then remove with a slotted spoon.

Melt the remaining 2 tablespoons of butter in a large skillet over medium-high heat. Add the remaining diced onions and cook for 3 minutes, then add the boiled pierogi and pan-fry for 2 to 3 minutes per side until beautifully golden and crispy.