In a large container, add the water and salt. Combine until the salt dissolves completely.
Add the first cup of precooked cornmeal.
Using your hands, begin mixing the ingredients. Be careful not to leave any lumps in the batter.
Add the second cup of flour and finish kneading until you get a smooth and uniform dough. Again, check for lumps. If you get any large lumps just flatten it with your fingers and knead again to get the perfect texture.
Place a large skillet or griddle over low heat and add the butter to melt.
Divide the dough into balls a little larger than a golf ball. With the palm of your hand, flatten the balls to create the shape of a thick tortilla. How flat should it be? It depends on each one, personally I like it very thin but remember that they will be stuffed so always leave enough thickness to open them in the middle.
Cook the arepas over low heat until golden brown on both sides. It is important that they are not cooked over high heat because they could burn on the outside and remain raw on the inside.
Repeat the process with all the dough and go placing the ones that are already ready in a large plate or basket.
Cut an opening in the middle of the arepa and stuff it with your choice of fillings.