Begin by preheating your oven to 425°F (220°C) and prepare a baking sheet by lining it with parchment paper to prevent sticking.
In a large mixing bowl, whisk together the flour, baking powder, salt, and freshly ground black pepper until well combined.
Introduce the cold, cubed butter to the flour mixture. Using a pastry cutter or your fingertips, work the butter into the dry ingredients until the mixture resembles coarse crumbs, with some small pea-sized pieces of butter still visible to ensure flakiness.
Gradually pour the cold milk into the flour mixture, stirring gently with a wooden spoon or spatula until just combined. Avoid overmixing; it's perfectly fine if the batter has some lumps.
Lightly flour your work surface and turn out the dough. Using a rolling pin, gently roll the dough into a rectangle about 1/2 inch thick.
In a separate bowl, combine the shredded mozzarella, finely grated Parmesan, garlic powder, and chopped parsley. Mix until evenly distributed, creating a delicious cheesy filling.
Cut the rolled-out dough into squares, approximately 3x3 inches in size. Spoon a generous amount of the cheese filling into the center of each square.
Carefully fold the corners of the dough over the cheese filling to create a pocket, ensuring to seal the edges tightly to prevent any filling from escaping during baking. Place the sealed biscuits seam-side down on the prepared baking sheet.
To achieve a golden and enticing finish, brush the tops of the stuffed biscuits with melted butter before placing them in the oven.
Bake in the preheated oven for 15-18 minutes, or until the biscuits are puffy and golden brown, filling your kitchen with a delightful aroma.
Once baked, allow the biscuits to cool slightly on the baking sheet. For an extra touch of flavor and shine, brush them with a little more melted butter and sprinkle with additional finely chopped parsley just before serving.
Notes
Serve warm with extra melted butter and parsley for garnish.