Place the panela and water in a small pot and cook over medium-low heat until the panela is dissolved completely and has a syrup consistency, then set aside.
In a medium bowl combine masarepa, panela mixture, beaten eggs, salt and melted butter. Knead with your hands until a dough is formed (add water if necessary), then cover and set aside for ten minutes.
Divide dough into 4 or 6 even pieces and roll into balls. Working on a wooden cutting board or a regular cutting board with a sheet of plastic wrap or parchment paper on top of it, flatten each ball down to a disk about ½-inch thick.
Heat a non-stick skillet over medium-low heat and add cooking spray. Add the arepas and cook, moving them around the pan, rotating them occasionally, about 3 minutes on each side, until a crust forms or they are golden brown. Serve hot with melted butter.