How to Make It
In a large bowl, mix the masa harina with 6 ounces of the feta and the salt. Slowly add the water while stirring with a wooden spoon. Add 3 tablespoons of the butter and stir until smooth. Turn the dough out onto a work surface and knead for 1 to 2 minutes or until it comes together in a smooth mass.
Set a cast-iron griddle over moderate heat. Divide the arepa dough into 4 equal pieces and roll each piece into a ball. On a clean work surface, flatten the balls of arepa dough and pat them into 5-inch rounds with smooth edges.
Spread 1 teaspoon of softened butter on 1 side of an arepa and set it on the griddle, buttered side down. Using a flat spatula, press the arepa into a 6-inch round about 1/3 inch thick; carefully smooth the edges if necessary. Cook the arepa over moderately low heat until browned, about 6 minutes; reduce the heat to low if the arepa browns too quickly. Spread the top of the arepa with 1 teaspoon of butter, flip and cook for 6 minutes longer, or until browned. Transfer the arepa to a plate, sprinkle with cheese and serve. Repeat with the remaining arepas.