Baked Bean Soup I've mentioned before. Both are incredibly cheap, yet burst with flavour, but this Red Lentil Soup beats it rival in the thrifty stakes as it's made from the bacon-y water left over from boiling a gammon aka ham stock!
It's adapted from a recipe in Soup Kitchen, a compilation with contributions from many renowned chefs, including Jamie, Nigella, Gordon and Rick, that was sold to raise money for homeless charities. Sadly it seems to be out of print but is still available through Amazon Marketplace or at a library near you.
Mr Lovelygrey gently fried three shallots, half a leek and crushed garlic until soft. He then added 500g of washed red lentils, a bayleaf, peppercorns and leftover bacon water. This was brought to the boil, simmered for forty minutes, blitzed in the food processor and seasoned. It can be thinned, as the recipe suggests with cream, milk or water if necessary.