- 1. Prepare the Dough: In a bowl, combine yeast, sugar, and warm milk. Let it sit for 5–10 minutes until foamy. Add flour and salt, then knead until a soft dough forms. Cover and let rise for 1 hour, or until doubled in size. 
- 2. Make the Filling: Mash the boiled potatoes while still warm. Mix in shredded cheese, butter, black pepper, salt, and garlic powder (if using). Stir until smooth and creamy. 
- 3. Assemble the Pie: Preheat oven to 375°F (190°C). Divide the dough into two equal portions. Roll out one half and place it in a greased baking dish. Spread the potato-cheese filling evenly over the dough. Roll out the second dough portion and place it over the filling. Seal the edges and brush with the egg yolk and milk mixture. 
- 4. Bake to Perfection: Bake for 30–35 minutes or until golden brown. Let it cool slightly before slicing and serving.