Peel the potatoes and cut them into 1 cm thick slices. Steam in a pressure cooker for about 6 to 7 minutes. Alternatively you can also boil the potatoes, in this case leave them whole, so they will absorb less water.
Heat oven to 180°C (350°F - Gas Mark 4)
Put the butter on the bottom of a bowl and mash the potatoes in the bowl.
Mix the potatoes when they are still hot with butter, eggs, grated Parmigiano, salt, pepper and nutmeg.
Grease a 20 cm round baking dish or a rectangular oven proof tray and spoon half of the mashed potatoes on the bottom. Cover the potatoes with ham and pieces of gorgonzola and top with the mashed potatoes.
Sprinkle the surface with breadcrumbs, then add slivers of butter and bake for about 40 minutes. Finish with 5 minutes of grill to make a crispy surface. Serve warm.
It's good also the next day, just warm it in the oven.