How to Make It
In a large bowl, mix the masa harina with the baking powder, 1/2 cup of vegetable oil and 3 cups of cool water. Knead the dough several times, then wrap it in plastic and let stand for 15 minutes.
Divide the dough into 16 pieces and flatten each into a 3-inch disk. Sprinkle the feta cheese over 8 of the disks. Top with the remaining disks and press the edges to seal. Gently press the arepas into even patties.
Heat 1/4 inch of oil in 2 large skillets. Add the arepas and cook over moderately high heat, turning once, until golden, 6 to 7 minutes. Drain on paper towels, then serve.