Place the mashed potatoes in a bowl and sprinkle them with flour. Mix with a spoon or your hands until a dough comes together. Form into patties that are about 1 inch thick.
Heat a skillet on medium-high heat and add the olive oil and butter. Place the mashed potato cakes in the skillet and let them brown on each side, about 3 to 4 minutes per side.
Top with warmed creamed spinach and a poached egg, and salt and pepper. Serve immediately.