Warm the milk until lukewarm (about 100°F or 37°C).

In a tiny bowl, mix together the milk, yeast, and sugar until well blended.

Let the mixture sit for 5-10 minutes, or until it becomes foamy.

In a large mixing bowl, combine the yeast mixture, melted butter, egg, salt, and 3 cups of flour.

Mix until the dough comes together, adding more flour as needed.

Work the dough for about 5 to 7 minutes until it reaches a smooth and elastic consistency.

Cover the dough with a clean kitchen towel and let it rise in a warm place for 1-1.5 hours, or until doubled in size.

Peel and chop the potatoes, then boil them in salted water until tender (about 10-15 minutes).

Drain and mash the potatoes with butter, cream, 1 1/2 tsp salt, and black pepper to taste.

In a frying pan, heat 2 tablespoons of butter over medium heat until it melts.

Add the diced sweet onion and sauté until soft and golden.

Add the Canadian bacon and cook for another 3-4 minutes, until lightly browned.

Stir the cooked onions, bacon, green onions, fresh dill, and grated mozzarella into the mashed potatoes. Mix well and set aside.

After the dough has doubled in size, deflate it gently and cut it into 12 to 15 equal portions.

Roll each piece into a small ball, then flatten into a 4-inch circle.

Place about 2 tablespoons of the potato filling in the center of each dough circle.

Fold the dough over the filling, pinching the edges together to seal, forming a half-moon shape.

Heat the canola oil in a deep frying pan or pot over medium-high heat to about 350°F (175°C).

Carefully add the piroshki in batches, frying for 2-3 minutes on each side, or until golden brown and crisp.

Remove from oil and place on a paper towel-lined plate to drain excess oil.

Serve the piroshki hot, garnished with extra dill or a side of sour cream for dipping. Enjoy!