Heat a large casserole (flameproof) dish over a high heat and add the meat. Break the meat up into small pieces until it browns. Add the onions and continue to fry for another few minutes.
Sprinkle over the flour, stir and blend in the Port and stock. Bring to the boil and stir until its thickened. Add the Wrocestershire sauce, redcurrent jelly, thyme and season with salt and pepper as desired.
Stir in the mushrooms, cover with a lid and cook in a preheated oven for about an hour and a half.
Remove from the oven and spoon into a 2 litre ovenproof dish and leave to cool slightly.
Put the potatoes into a large saucepan, cover with water and bring to the boil. Add the butter and milk, heat and mash until smooth.
Spread the mash potato over the mince to completely cover the beef. Then drag a fork over the top to create a nice pattern if you like!
Cook in a preheated oven for about 30-35 mins until lightly golden and bubbling around the sides.