Arepas two ways: from whole corn cooked overnight and ground by hand, or from precooked cornmeal in five minutes. The first is how grandmothers made them and it starts the day before.
Two completely different recipes share this page. The first starts the night before with a kilo of whole shelled corn, cooked for an hour and left to rest overnight, then ground into dough. The second is two cups of precooked cornmeal and two cups of water, and it takes five minutes. Both make arepas and only one of them tastes like the arepas people remember. Drain the corn properly before grinding. It is the one thing that ruins the traditional method: corn that goes into the grinder wet produces a slack dough that will not hold a disc, and there is no way to recover it except adding precooked cornmeal, which defeats the purpose. Ten minutes a side is a long roast and it is right for an arepa this thick over embers. What you are looking for is a dry, blistered crust with the inside cooked through. On a griddle it goes faster, so check earlier. Masarepa and areparina are the same thing under different names: corn that has already been cooked and dried, so it only needs water. Ordinary cornmeal or corn flour will not work.