Mix the cold rice with the egg and form medium-sized balls. Put a mozzarella cheese cube in the middle of each ball and lay in the buttered muffin tin. Continue until all ingredients were used. Bake for about 20 to 30 minutes until the muffins are well puffed and golden brown. Let them cool. Remove them from the molds. For the frosting, mix the cheese with the Parmesan cheese and nutmeg.
Garnish the muffins using a spoon or pastry bag and top with the pistachio crumbs.