I always make too much oatmeal, because it is better than making not enough oatmeal. But oatmeal leftovers used to seem kind of useless to me as I couldn't find a good way to reheat them. A few years ago I found this idea on a blog, and have since seen the idea in Nourishing Traditions. It is very basic - add an egg or two to your leftover straight from the fridge cold oatmeal. I mix the egg(s) into the oatmeal with a fork and the oatmeal clumps fall out pretty easily. I melt butter in a pan and drop scoops of the oatmeal onto the pan. Flatten the oatmeal out a bit with a spatula, as you don't want it too thick in the middle. I fry on both sides until they are golden and crispy and then serve with a little maple syrup on top. These are really yummy and good for breakfast or snack.
