Faina Merzlyaks Potato and Mushroom Pierogi

Make the dumpling dough: Lightly beat the yogurt, egg, and salt together with an electric mixer. Slowly add the flour and continue beating until smooth. Knead the dough on a floured surface until smooth. Add water, a teaspoon at a time, only if needed to smooth out the dough; it should feel like pizza dough. Form the dough into a ball, wrap it in a kitchen towel, and set aside in a cool place for 2 hours.

Meanwhile, make the filling: Peel and quarter the potato. Cover with cold water, bring to a boil, lower the heat, and simmer until it offers no resistance when pricked with a fork, 15 to 20 minutes. Drain and set aside.

Melt 2 tablespoons of the butter in a skillet over very low heat. Whip the potato with the butter until it is fluffy and creamy. Set aside.

Melt the remaining 2 tablespoons butter in the skillet over medium heat. Add the onion and saut until translucent, 5 minutes. Add the mushrooms, salt, and pepper and saut until the mushrooms are tender and any liquid exuded by the vegetables evaporates, about 5 minutes. Remove the mixture from the skillet and set aside to cool slightly. Mix the vegetables into the mashed potatoes.

Bring a large pot of salted water to a boil.

Meanwhile, roll out the dough 1/8 inch thick. Cut into 3-inch rounds with a cookie cutter or the rim of a glass. Put about 1 heaping teaspoon of the mashed potato filling on one side of the circle. Fold the other side over the filling so the pierogi looks like a half moon. Press the edges together with your thumb and index finger, sealing the pierogi.

Lower the heat so the boiling water simmers gently. One at a time, add the pierogis to the water in batches of 4 to 6. Simmer until cooked through, 5 to 7 minutes. Remove with a slotted spoon and drain on paper towels. Keep warm while cooking the remaining pierogis. Serve with fried onions or sour cream.