Baked Yeasted Pierogi with Buckwheat, Twaróg, and Mint from Fresh From Poland: New Vegetarian Cooking from the Old Country by Michał Korkosz

Ingredients

• 2½ cups (320 g) all-purpose flour, plus more for shaping
• One ¼-ounce (7 g) packet instant yeast
• 1 tablespoon sugar
• ½ cup (100 g) whole buckwheat (kasha)
• 2 tablespoons (30 g) unsalted butter
• 1 medium white onion (5 ounces/150 g), chopped
• 3 garlic cloves, sliced
• 1 cup (170 g) crumbled farmer cheese or Twaróg
• ½ teaspoon dried mint
• Salt and freshly ground black pepper
• 1 large egg
• 1 tablespoon milk
• 1 tablespoon cold-pressed rapeseed oil
• Flaky sea salt
• Fresh mint leaves