For an excellent supper or lunch you will need:

Remains of Sunday’s pheasant casserole. (This will be largely vegetables in sauce, ‘cos you ate all the pheasant, right? It’ll still make good soup.)
Leftover potatoes, chopped into 5mm dice
2 small or 1 medium onion, chopped finely
Some vegetable or chicken stock or a couple of glasses of white wine
Small glass of port, brandy or similar (optional)
Cream (optional)
Chopped herbs (optional)
Grated Parmesan (optional)
Seasoning

Sweat the diced potatoes and onion in a drizzle of olive oil until the onion is somewhere between translucent and caramelised (according to your taste).
Meanwhile put the remains of the casserole in the blender and whizz until smooth.
Add the blended casserole to the frying onion & potato.
Bring gently to the boil and simmer for 10-15 minutes, adding wine or stock as required to keep it of a soupy consistency.
At this point you can turn out the heat and leave the soup until you’re almost ready to eat.
When ready return the soup to the simmer, add the port/brandy and the tomato paste.
Season to taste and return to the simmer.
Serve in a tureen or individual bowls with a swirl of cream, chopped herbs and grated Parmesan, and accompanied by good crusty bread and butter.