Mix the mashed potato, sausagemeat and flour together in a mixing bowl. Add salt and freshly ground black pepper to taste and mix well.
Using your hands, shape the mixture into eight round patties and press one sage leaf onto the top of each patty.
Heat the oil in a frying pan. Place the patties sage-side down into the oil and fry for 4-5 minutes each side until the patties are golden-brown and cooked through in the middle. Serve straightaway.