Bean and Cheese Pupusas

For masa (dough): Place masa flour in a large bowl. Gradually stir in the warm water to form a dough, kneading dough gently until smooth, 2 to 3 minutes. The masa will have a texture like firm play dough. (Test masa by taking a small handful and forming it into a ball then flattening it. If masa cracks, add water, 1 tablespoon at a time, until dough is moist enough.) Cover with a damp cloth; set aside.

In a medium bowl, toss together mozzarella, melted butter, pepper and salt until well mixed.

To assemble pupusas: Divide masa into six equal portions (about 2 1/2 ounces each). Working with one portion at a time (and keeping remaining portions covered with the damp towel), flatten masa in your palm, simultaneously twisting and slapping it into a 6-inch-diameter tortilla-like shape. Holding the flattened masa in your hand, add 2 1/2 tablespoons refried beans and a heaping 1/4 cup of the cheese mixture. Reform dough into a ball shape, enclosing the fillings. Gently flatten filled ball into a thick disk, 4 1/2 to 5 inches in diameter. (This takes practice. If the fillings peek through in spots, don't worry about it. Alternately, place pupusa ball inside a cut-open resealable freezer bag and gently flatten ball on the counter instead of between your bare hands.) Repeat with remaining masa and fillings, covering completed pupusas with another damp cloth. After you've formed your first pupusa, heat a large skillet over medium. Brush skillet with some of the oil.

To cook: Place a pupusa in the hot skillet. Cook until the outer edge of pupusa changes from pale white to light brown. Flip pupusa and repeat, cooking the second side until light brown and free of any pale dough, 5 to 7 minutes total. Repeat with remaining pupusas, re-oiling skillet between batches. Drain on paper towels. Serve hot, topped with Red Salsa and Curtido.