Ground Beef-stuffed Potato Pierogis

For the dough, rinse potatoes and cook in boiling salted water for 20-25 minutes. Drain and peel potatoes and press through a potato ricer. Let potatoes cool briefly.

Mound flour in a bowl and make a well in the center. Crumble yeast into well in flour, stir in sugar and a little water and mix to a paste. Cover bowl and let stand for about 15 minutes. Add potatoes, remaining water, 1 teaspoon salt and oil to flour mixture and knead to a smooth dough. Cover dough and let stand at room temperature for about 30 minutes.

For the filling, peel and dice onion and garlic. Heat oil and sauté beef. Add onion and garlic to beef and sauté. Rinse and trim leek, cut into rings, stir into beef mixture and season with salt and pepper.

Knead dough briefly and roll out on a lightly floured surface. Cut 12 circles about 14 cm diameter (approximately 5 1/2 inches) from dough. Spoon filling mixture onto centers of dough circles. Brush edges of dough circles with water and fold circles over to cover filling, forming pierogis. Firmly press edges of pierogis with the tines of a fork to seal.

Place pierogis on a baking sheet lined with parchment paper. For brushing, whisk egg yolk with milk and brush over pierogis. Bake pierogis in oven preheated to 200°C (fan: 180°C, gas mark 3-4)(approximately 400°F) for 20-25 minutes.