With a sharp knife, cut the courgettes lengthways into slices (¼ inch thick); you should get 4-6 slices from each courgette.
Cook the courgette slices in plenty of lightly salted boiling water for about 2 minutes, until just tender, then remove and plunge into cold water. Drain and dry on kitchen paper.
Preheat the oven to 240c. In a large bowl, mix the ricotta, mashed potatoes, Parmesan and some salt and pepper. Take 2 slices of courgette, place them on a clean, dry surface and shape them in a cross. Repeat with the rest of the courgette slices.
With your fingers, shape the ricotta mixture into balls about the size of a ping-pong ball (one for each courgette cross). Place a ball in the middle of each cross, place a sage leaf on top and then fold the strips of courgette over to make a parcel. Place a slice of Fontina cheese on top and secure with a wooden toothpick. Line a baking tray with foil or greaseproof paper and grease with some butter. Place the courgette parcels on the baking tray (At this stage you can refrigerate and cook when needed.) Bake for 10-12 minutes, until golden.
Remove the parcels from the oven, place on a serving dish and remove the toothpicks. Serve warm with some salad leaves