In a mixing bowl, combine bread flour, room temperature egg, warm milk, instant dry yeast, sugar, salt, and melted unsalted butter. Knead the dough until smooth and elastic. Cover and let it rise in a warm place until doubled in size.
Boil the potatoes until tender. Peel and mash them in a bowl. Season the mashed potatoes with salt, pepper powder, and heavy cream or milk. Mix well. Fold in mozzarella cheese into the potato mixture.
Punch down the risen dough and divide it into two portions. Roll out one portion into a circle to fit a 24cm diameter pan. Spread the potato and cheese filling evenly over the dough circle. Roll out the second portion of dough and place it on top of the filling. Seal the edges tightly.
Place the assembled bread in the pan. Brush the top with milk. Cover and let it rise again for about 30 minutes. Preheat your oven to 180°C (350°F). Bake the bread for 25-30 minutes or until golden brown and cooked through.
Brush the freshly baked bread with melted unsalted butter. Garnish with chopped parsley if desired. Allow the bread to cool slightly before slicing and serving.
