Boil the potatoes, peel and mash them. Add the spices, egg, butter and knead well. Lay out the mixture in a buttered form. Bake at 392°F (200 °C) for 30 min. or until golden.
In the meantime, cut the meat into small pieces and fry them. Add the mushrooms and spices. After a few min., pour in the cream and chopped cheeses.
Stir well until they melt. Take the tartlet out, let it cool a little and invert it onto a suitable plate. Pour the filling on top and sprinkle generously with mozzarella (or cheese).
Return to the oven for a few min. for the mozzarella to melt. Leave it cool a bit and serve.