Instructions:
- Prepare the Dough: Combine the flour, baking powder, and salt in a large bowl. Make a well in the centre and add the low-fat yogurt. Mix vigorously until a shaggy dough forms.
- Knead Briefly: Turn the dough onto a lightly floured surface and knead gently for 2-3 minutes until smooth. Cover and allow to rest for 10 minutes.
- Sauté the Filling Base: While the dough rests, lightly sauté the sliced mushrooms in a dry frying pan until they have released their liquid and browned slightly. Set aside to cool slightly.
- Assemble the Filling: In a bowl, mix the cooled mushrooms, diced ham, oregano, and most of the mozzarella (reserving a small amount). Stir well to combine.
- Divide and Roll: Preheat your oven to 400°F (200°C / Gas Mark 6). Divide the rested dough into 4 equal portions. Roll each portion into an oval or circle, about ¼ inch thick.
- Fill and Seal: Place a quarter of the filling mixture onto one half of the rolled dough, leaving a generous border around the edges. Brush the edges with a little water.
- Fold and Crimp: Fold the empty half of the dough over the filling to create a half-moon shape. Firmly press the edges together to seal, crimping them with your fingers or a fork to prevent leakage.
- Glaze and Bake: Place the calzones on a baking sheet lined with parchment paper. Brush the tops lightly with the whisked egg white. Make a small slit in the top of each calzone to allow steam to escape.
- Cook: Bake for 18–22 minutes, or until the calzones are puffed up and golden brown.
- Serve: Allow to cool for 5 minutes before serving immediately, perhaps alongside a small bowl of warmed passata for dipping.