Mix arepa flour, salt, sugar, and mozzarella in a large bowl. Add hot milk or water and stir until combined. Let mixture stand until milk is absorbed enough for a soft dough to form, 1 to 2 minutes. You can estimate how much of each depending on how you want your dough (Thicker–> more flour, sweeter–> more sugar). Once they are formed into patties, make sure theres enough cheese inside, and fry them in a pan with enough oil or butter to keep them from sticking.