Heat a griddle pan (or ordinary frying pan). Lay the chicken breasts flat on a board and, using a sharp knife, slice each one horizontally to give 3 flat pieces.
Cook 4 pieces of chicken for 5 minutes on each side. When cooked, arrange these on an oiled baking sheet – these will form the base of the stacks. Put a few sage leaves on top of each one and season.
Cut each length of prosciutto in half and cook 4 pieces for 4 minutes on each side. Place these on top of the chicken. Cut each slice of fontina in half. Top each chicken and prosciutto stack with a piece of cheese.
Griddle or fry the remaining chicken and prosciutto and stack up as before with the cheese and sage, completing each stack with a final layer of chicken. Place the baking sheet in a preheated oven, 180°C (350°F), Gas Mark 4, and cook until the cheese is soft, about 5–8 minutes.
Drizzle with a little olive oil, sprinkle with salt and pepper and garnish with a few sage leaves. Serve with freshly cooked pasta tossed in butter and black pepper.