In a large mixing bowl, combine the flour, baking powder, and salt. Add the cold butter and use a pastry cutter or your fingers to mix until the mixture resembles coarse crumbs.
Stir in the mozzarella and ricotta cheese until evenly distributed throughout the flour mixture.
Add just enough cold water (about ¼ cup) to bring the mixture together into a cohesive dough. Avoid overworking it. Wrap the dough in plastic wrap and refrigerate for 30 minutes.
Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
On a lightly floured surface, roll out the chilled dough to about ¼-inch thickness. Cut out circles using a large biscuit cutter or a glass (about 4 inches in diameter). You should have about 8-10 circles.
Place a circle of dough on the prepared baking sheet. Scoop a tablespoon of pizza sauce into the center, top with a mix of your chosen toppings, sprinkle some Italian seasoning, and add more mozzarella cheese on top.
Place another circle of dough over the top and press down the edges to seal. Use a fork to crimp the edges securely and create a decorative pattern.
Beat the egg in a small bowl and use a pastry brush to coat the tops of the pizza pockets. This will give them a golden color when baked.
Bake in the preheated oven for 15-20 minutes, or until the pockets are golden brown and firm to the touch.
Let them cool for a few minutes before serving. Serve warm with extra pizza sauce for dipping.
Notes
Arrange the cheesy pizza pockets on a platter, served with a small bowl of pizza sauce for dipping, and garnish with fresh basil leaves for a pop of color.