1. In a large bowl, mix together the flour and salt. In a separate bowl, whisk the egg, sour cream, and melted butter. Combine wet and dry ingredients until a shaggy dough forms. Knead on a lightly floured surface for about 5–7 minutes, until smooth and elastic. Wrap and rest at room temperature for 30 minutes.

2. Combine shredded cheddar with mashed potatoes (if using), and season with salt and pepper. The potatoes help bind and soften the cheese for a meltier center.

3. Roll out the dough to about ⅛ inch thick. Cut into circles using a cookie cutter or glass (about 3 inches). Place 1 tsp of filling in the center of each round. Fold into a half-moon and pinch the edges tightly to seal.

4. Bring a large pot of salted water to a boil. Boil pierogi in batches until they float (2–3 minutes), then cook 1 more minute. Optionally, pan-sear them in butter for crispy edges.

5. In a large skillet, melt butter over medium heat. Add sage leaves and garlic; cook until butter foams and turns slightly golden, and sage is crispy (about 2–3 minutes). Stir in cream and reduce heat to low. Let simmer for 1–2 minutes. Season with salt, pepper, and a squeeze of lemon (if using).

6. Add cooked pierogi to the pan with the sauce and gently toss to coat. Plate with extra sauce spooned over top, and garnish with extra sage, black pepper, or Parmesan.