In a medium bowl, combine masarepa, sea salt, Cotija cheese, softened butter, and warm water. Stir until mixed and a smooth dough forms, about 5 minutes. Allow the dough to rest for 10 minutes.

With lightly wet hands, divide the rested dough into 8 equal pieces. Shape each piece into a circle about 5 inches wide and ¼ inch thick.

Take one dough circle and add a generous amount of shredded mozzarella cheese in the center, ensuring you leave space around the edges to seal. Carefully place another dough circle on top and gently pinch the edges together.

Heat oil in a skillet over medium-low heat. Place your filled Arepas con Queso in the skillet. Cook for 4-5 minutes on each side until they turn golden brown.

Once golden and crispy, carefully remove the Arepas con Queso from the skillet and let them drain on paper towels. Serve warm.