Prepare the macaroni and cheese and pour it into a pan - a 9"x5" loaf pan works well, or a 9"x9" square pan. Cover and refrigerate overnight, or until solid.
When ready to fry them, put the flour, eggs and Panko in three shallow dishes; beat the eggs a little with a fork. Heat the oil in a deep pot until a bit of bread sizzles when put in, but the oil is not smoking. Cut the macaroni and cheese into blocks about 1" x 1 1/2", roll each in flour to coat, then dip in the egg, and coat in breadcrumbs. Fry in the hot oil until crispy and golden. Transfer to paper towels to drain. Serve warm.