Preheat oven to 350 degrees. Generously butter a 9-inch dish. Peel the potatoes then cut into rough chunks.
Place the potatoes, sliced garlic and a good amount of salt in a large pan and set over a medium high heat. Cover with cold water and bring to a boil.
Simmer until the potatoes are completely tender.
Drain the potatoes and allow to steam for 5 to 10 minutes to allow all the excess moisture to disappear.
Heat the milk and butter until melted.
Pass the potatoes through a ricer and add the milk and butter mixture, season with salt and pepper and mix to combine.
Transfer mixture to prepared pie dish. Sprinkle the potatoes with Parmesan cheese then place mozzarella slices over the top. Sprinkle rosemary, thyme, oregano, salt and pepper on top of the mozzarella then bake 30 minutes or until the cheese is golden brown and bubbly. Let the pie sit for a few minutes before serving