Wash, cut and boil the potatoes until ready in salted water. Strain them and while still warm, mash them with the butter and leave them to cool. Make the meat filling. Wash and finely chop the onions and carrot.
Heat the olive oil in a pan on the stove and braise the onions and carrot briefly. Add the mince, break it up with a spatula. Fry until the mince is ready, sprinkle with cumin and black pepper to taste at the end.
Divide the potato mixture into 2 equal parts. Pour one part of it at the bottom of the oven dish and even it out, making sure to cover the entire bottom.
Pour the meat filling evenly on top, cut the mozzarella into slices and arrange them on the mince. Pour on the rest of the potato mixture on top, even it out once again. The mince and mozzarella need to be well covered.
If desired, use a fork to make random stripes along the potato mixture and then put the oven dish in a preheated 356°F (180 °C) oven for 30 min. to bake. Finally, take it out from the oven, wait for it to cool and cut into servings.