Place the potatoes in a large pot and pour cold water over them to cover. Bring it to boil. Let it simmer uncovered until tender, for about 20 minutes. Check tenderness with a fork or knife. Drain.

Peel and mash the potatoes. Add in milk, cream cheese, grated mozzarella, salt and black pepper. Stir the mixture until combined well. Depending on the type of potatoes, you might need to add extra hot milk, 1 tablespoon at a time so that it becomes as creamy as you desire.

For the topping, heat olive oil in a small pan and saute crumbled walnuts or any nut you like just until they start to smell, for about 5 minutes. Top mashed potatoes with roasted nuts and optionally sprinkle extra black pepper over it.