Garlic-Parmesan Potato Pierogi, Basil Yogurt

Steps

1. Make the dough: in a bowl, mix the flour with half of the salt. Add the egg, warm milk, water and one-third of the olive oil; stir, then knead 5 minutes until smooth. Cover and rest 30 minutes.
2. Meanwhile, make the filling: boil the potato in a large pot of water until fork-tender, about 15 minutes. Drain well, keeping the pot of hot water off to the side for later, and mash.
3. In a large skillet over medium-low heat, warm another one-third of the olive oil and cook the garlic 1 minute until fragrant. Stir the garlic into the potatoes with the mozzarella, Parmesan, black pepper and the remaining half of the salt. Let the filling cool. Wipe out the skillet.
4. Make the herb yogurt: stir together the Greek yogurt, basil and lemon juice. Chill until serving.
5. Roll the dough about 1/8 inch thick and cut 3-inch rounds, rerolling scraps, to make about 28. Place a spoonful of filling on each, fold into half-moons and pinch the edges firmly to seal.
6. Bring the pot of water back to a boil. Cook the pierogi in batches until they float, then 2 minutes more. Lift out with a slotted spoon.
7. In the skillet over medium heat, warm the remaining one-third of the olive oil and cook the red onion until soft and golden, about 8 minutes. Push it aside, add the boiled pierogi and fry 2 minutes per side until golden.
8. Serve the pierogi topped with the red onion, with the basil yogurt alongside.