Bring the milk to a boil in a small pan. Add butter. Let stand and cool slightly.
Grind frozen yellow corn kernels in a food processor. You can find arepa flour at many Latin and Mexican markets. If there isn’t one near you, grind corn meal 1/4 cup at a time in your blender, and add 1/2 cup of flour.
In a large bowl, mix the ground corn, arepa flour or cornmeal, salt, sugar, and mozzarella. Make a well in the center and gradually add the hot milk and butter mixture. Stir until there are no lumps. Work the dough until it is smooth and sticky.
Take the rest of the butter and heat it on a frying pan. Drop arepa mix in rounded tablespoon fulls on to the pan. Fry on each side 3-5 minutes until browned.
To serve, butter the arepa and dd extra grated mozzarella cheese or queso blanco on top. If you made the arepa slightly larger, you can cut a slit in the middle and stuff them with the cheese. Otherwise, you can take two arepas, add the cheese in the middle and eat them like a sandwich.
You may also make the pancakes only and store them in the refrigerator or freezer until ready to serve. Just lightly butter two pancakes, put a slice of cheese in between, and heat on the griddle at low heat until the cheese melts.