Heat a tbsp of vegetable oil in a pan. Cut the chicken breasts in chunks and add them to the pan and fry until brown. Remove the chicken from the pan and set aside. In the same pan, sauté the chopped leek and carrots until soft, then add the chicken and mix well. Pour 1 1/2 cup of milk and add 1 tbsp of plain flour and mix until the milk thickens into a sauce. Transfer to an oven-proof dish. Season well and leave to cool. Roll the ready- made pastry and cut it into a circle or the shape of your dish, if different. Brush the edges of the pastry with oil. Sprinkle semolina on top of the dish, that will prevent the pastry from becoming soggy. Place the pastry on top and bake in the preheated oven until golden-brown.