Potato and Cheese Pierogi

For the Filling: In a medium skillet, melt 2 tablespoons (30g) butter over medium heat. Add onion, season with salt and pepper, and cook, stirring frequently, until softened, about 5 minutes. Continue to cook, stirring frequently and adding 1 to 2 tablespoons (15 to 30ml) of water at a time when onions begin to stick and threaten to scorch, until light golden-brown, about 15 minutes. Vicky Wasik Meanwhile, in a large saucepan, combine potatoes, 2 quarts (1.9L) water, and 2 teaspoons (6g) salt. Bring to a boil over high heat, then reduce heat to maintain a simmer. Cook until potatoes are tender and offer little resistance when pierced with a paring knife, about 10 minutes. Drain potatoes, and return to now-empty saucepan. Set saucepan over low heat and cook, shaking constantly, until moisture has evaporated from potatoes, about 1 minute. Remove from heat. Vicky Wasik Using a ricer or food mill, pass potatoes into a medium bowl. Using a flexible spatula, stir in remaining 3 tablespoons (45g) butter, and 1/2 cup (115g) of the reserved onion mixture; transfer remaining onion mixture to a small bowl for garnish. Season with salt and pepper to taste, and allow to cool for 5 minutes. Stir in farmer cheese until thoroughly combined, cover, and set aside if making the pierogi right away, or refrigerate filling for up to 2 days. Vicky Wasik For the Dough: Whisk together flour and salt in the bowl of a stand mixer until thoroughly combined, at least 30 seconds. Add sour cream and egg, fit stand mixer with dough hook, and mix on medium-high speed until a smooth and elastic dough forms that pulls away from the sides of the bowl, 6 to 8 minutes. Cover, and set aside at room temperature for at least 30 minutes or wrap in plastic and refrigerate for up to 24 hours. Vicky Wasik To Assemble and Finish: While dough is resting, portion the potato filling. Using a 1-tablespoon measuring spoon, scoop 1 heaping tablespoon (1 ounce; 30g) portions of potato mixture onto a rimmed baking sheet. Roll each portion between your palms to form a ball and set back on baking sheet. Line a second rimmed baking sheet with parchment, and dust lightly with flour; set aside. Vicky Wasik Once dough is rested, turn out onto a lightly floured surface. Using a rolling pin, roll dough into a roughly 18-inch circle, about 1/8-inch thick. Using a 3-inch cookie cutter, punch out 24 rounds of dough. Place one portion of filling in the center of each round of dough. Working with one portion of dough at a time, fold dough over filling to form a half-moon while distributing filling to fit within it, firmly pinch edges to seal, and transfer to prepared baking sheet. Repeat with remaining portions. Uncooked pierogi can be covered and refrigerated for up to 24 hours. Vicky Wasik In a pot of boiling salted water, cook half of the pierogi until dough is cooked through and filling is heated through, 3 to 5 minutes. Using a spider skimmer, transfer to a lightly greased baking sheet. Repeat with remaining pierogi. Boiled pierogi can be served as-is with reserved cooked onion and sour cream, or proceed to step 8 for pan-frying instructions. Vicky Wasik In a large nonstick skillet, heat 1 tablespoon (15ml) vegetable oil and 1 tablespoon (15g) butter over medium-high heat until butter is foaming. Add enough pierogi to cover the bottom of the skillet in a single layer without crowding the pan, and cook, flipping occasionally, until crisp and golden brown on both sides, 3 to 5 minutes. Transfer to serving platter. Repeat with remaining pierogi, adding remaining oil and butter as needed. Serve, passing sour cream, reserved onion, and chives (if using) at the table. Vicky Wasik