I have always been wary of breading things (coating them in breadcrumbs and frying them, I mean). The breadcrumbs never form an even layer; they fall off; they stick to your hands. Nevertheless, if you expect that to happen, and learn to be relaxed about it, you can get reasonable results.
I had a cereal bowlful of leftover mashed potato, and slightly more leftover kale. (Equal quantities would have been ideal, but the imbalance did not matter.) I put some flour on a plate, beat an egg in a bowl, and, in a third bowl, put about 5 tbsp of breadcrumbs. I added some pepper to the mash, which I merged with the kale and formed into two patties the size of chunky hamburgers.
I warmed a frying pan, and heated a layer of sunflower oil until a breadcrumb started sizzling in it. (The heat means that the potato cake will form a crust quickly, and therefore will not absorb a huge amount of oil.) I turned the patties in the flour, then in the egg, then in the breadcrumbs, and fried them for about three minutes on each side. The flour helps the egg to stick; the egg helps the breadcrumbs to stick.
As I have written before, potato cakes of this size will brown before they are warmed through. I transferred them to a baking sheet, and put them into a gas mark 6/200 C oven for 10 minutes.