Thaw the frozen dough. Preheat the oven to 392°F / 200°C. Cut the chicken into strips, quarter the mushrooms and chop the spring onions. Have some chicken stock prepared in advance. When the oil is hot, add chicken and fry. Then add the spring onions and mushrooms. Season with salt and pepper. Add the flour, sour cream and mustard. Stir together and pour the chicken stock into it. Add some basil as well. Pour the mixture into the baking tray.
Roll out the thawed dough with the rolling pin to the size of the baking tray so that it covers the surface. Fold excess dough over to tuck inside the pan so there is no filling left uncovered. Brush the egg wash over the surface of the dough. Use a sharp knife to cut 5-6 slits in the top crust. Put the baking tray into the oven and bake for about 20 minutes until golden brown.