Peel and chop raw potatoes and boil in salt water with a clove of minced garlic and a bay leaf if you’d like, until fork tender. Drain potatoes and let dry; discard the bay leaf.
Chop onions and raw bacon slices into pieces. Sautee in stock pot until bacon is done and a little crisper than you would normally make it. This is because once liquid gets in the bacon becomes softer.
Drain off most of the bacon fat. Over low heat, add leftover mashed potatoes, gradually working in milk until the chowder is easy to stir; you can always thin it a bit at the end if you want to. Here you can add shredded cheddar cheese (as much as you like), and any leftover ham or Canadian Bacon pieces, etc. Stir until cheese is fully melted and incorporated. Add your chunked cooked potatoes and stir gently. The cheese and potato chunks will thicken the chowder a bit; it will also thicken as it cools.
Heat until potato chunks are heated through and serve. This makes a very filling dinner with a salad and crusty French bread or garlic bread. If you have room for anything else, it’s good with peaches on the side, or even a cobbler.