Times of need call for resourcefulness and creativity, and it is out of that need that bubble and squeak was born. Bubble and squeak became popular during the Second World War when rationing was in effect throughout Britain and the need to stretch every morsel of food was a necessity. Taking whatever was left after a roast and frying into a cake (or sometimes hash) made those leftovers into an entirely new meal without wasting anything from the previous dinner.
'potato cakes' on Serious Eats
If you find yourself in the position of having too many leftover potatoes and not enough gravy, these simple cakes makes a quick crisp brunch. As they cook, the potatoes and cheese tend to get soft, so be gentle when flipping. A bloody mary and couple of potato cakes will surely take the edge off any sort of post holiday drowsiness.