Sausage pie, simple as!
Chop your onion, sausages, and mushrooms and place in a pan with some oil. Put potatoes on to boil (boil them until they are ready to be mashed).
when sausages are cooked, add your gravy and tomato puree and stir together.
add pepper, salt, some garlic and red wine for taste.
cook it all until the potatoes are ready to be mashed. Mash them, and put the mixture into a casserole dish. Put mashed potato on top, and pop in the oven for a few minutes to keep warm.