Preheat oven to 220°C (200ºC fan assisted)/ Gas 7.
Heat the butter and half of the oil in a large pan and gently fry the onions, garlic and bacon until the onions are soft. Remove from the pan and put aside. Add the rest of the oil and heat through, then quickly brown the beef.
Stir in the flour, then beer and orange juice and zest. Return the onions and bacon to the pan with the carrots and stir well, add sufficient stock to just cover, season and bring to boil. Simmer for approx. 45 min. until the meat is tender, stirring occasionally to prevent sticking.
At the end of the cooking time add the mushrooms, then allow to cool thoroughly and place in a pie dish. Place a pie funnel or upturned egg cup in the centre to help support the pastry.
Roll out the pastry large enough to cover the dish with some room to spare. With a sharp knife cut strips of pastry from edges and use to form a rim on the pie dish edge. Brush edge with beaten egg to help the pastry stick, then brush the pastry rim with egg wash.
Carefully lift the pastry, lay over the pie dish and press down edges to form a good seal and trim off excess with a sharp knife. Reserve trimmings. Knock up and flute the edges of the pie and make a hole in the centre over the pie funnel to allow the steam to escape.
Re-roll trimmings and cut out leaves or other shapes of your choice. Brush the pastry top with egg wash, arrange leaves on top and brush again. Bake for approx. 40 minutes until pastry is risen and golden brown.