Heat olive oil in a non-stick saucepan; add in leek and garlic and fry for 20-30 seconds. Put in bacon and continue to fry for 1-2 minutes until soft. Add mushrooms and chicken. Fry and cook until mushrooms are soft.
Combine cornflour with about 1-2 tablespoons of the chicken stock and add to the chicken and mushroom mixture. Pour in remaining chicken stock and cook till it boils. Reduce the heat and simmer for 1-2 minutes, then pour in the whipping cream. Stir well to mix for 30-40 seconds. Dish out. Add parsley, salt and pepper to taste. Leave aside to cool then refrigerate for 2-3 hours before use.
Lightly grease ramekins with butter. Using the tops of ramekins as a guide, cut out 3-4 rounds from the sheet of puff pastry. Divide the portion of filling between ramekins and fill up to about ¾ full. Place the pastry circles on top of the filling. Use a fork to seal the edges then pierce a small hole in the centre of each top.
Brush lightly with beaten egg. Arrange the ramekins on a baking tray and bake in preheated oven at 200°C for 18-20 minutes or until the top is puffed and golden brown. Serve immediately.