When my husband makes mashed potatoes, he makes mashed potatoes - we have them for days on end. I found this recipe in the "Staff Meals from Chanterelle" cookbook and made it my own; it calls for making your own mashed potatoes, but I used the leftover ones. I am not including the instructions for making the mashed potatoes, as I will always be using his own ones (so sub your own recipe).
However - this was an absolutely DELICIOUS take on comfort food, perfect for a chilly night. It also went very quickly in terms of prep (no making of mashed potatoes, remember), making it easy for a weeknight meal. We loved it, and I love that I could use ketchup on it. Every time we make mashed potatoes for something else, we're making this the next night (but I would also make mashed potatoes for it, it was that good).