Leftover Potato and Cheese Pierogi

Combine flour and salt in a large bowl. Make a well in the center and crack in the egg. Add water gradually, mixing with a fork until a shaggy dough forms.

Knead the dough on a floured surface for 8 minutes until smooth and elastic. Wrap in plastic and rest at room temperature for 30 minutes.

Melt 2 tablespoons butter in a skillet over medium heat. Sauté the diced onion until translucent and lightly golden, about 5 minutes. Let cool slightly.

In a large bowl, combine the leftover mashed potato, sautéed onion, and grated cheddar cheese. Mix until evenly incorporated. Season with salt and pepper to taste.

Divide rested dough in half. On a floured surface, roll each portion to 1/8-inch thickness.

Using a 3-inch round cutter or inverted glass, cut out circles. Spoon about 1 tablespoon of potato-cheese filling into the center of each circle.

Fold dough over filling to create a half-moon. Crimp the edges firmly with a fork to seal. Transfer to a floured surface. Repeat with remaining dough and filling.

Bring a large pot of generously salted water to a boil. Carefully drop pierogi in batches and cook until they float to the surface, about 3-4 minutes. Remove with a slotted spoon to a parchment-lined plate.

In a large skillet, melt remaining 3 tablespoons butter with olive oil over medium-high heat. Add boiled pierogi in a single layer and fry until golden brown on each side, about 2-3 minutes per side.

Arrange crisp-fried pierogi on a warm platter. Dollop with yogurt, scatter fresh parsley, and serve immediately while the cheese center is still pulling taut.