Preparing the Corn Masa Dough:Place the corn masa flour in a shallow bowl. Mix in the water, 1 cup at a time, kneading by hand for about 10 minutes until the dough is moist and fluffy. If needed, add more water 1 tablespoon at a time. The dough can be prepared the day before, if covered and refrigerated. Making the Pupusas — Method 1:Divide the dough into 12 equal small balls. Divide the filling equally for the 12 pupusas. Take the dough ball in the palm of your hand, pushing the center of the ball with your fingers to make a well. Fill each pupusa with the cheese filling. When done, close the top by pushing and pinching the open space together, so that the end result will be a completely filled and sealed dough ball. Wet your hands, press and pat each ball between your palms and flatten into a thin dough round that is about 4 inches in diameter and ¼-inch thick. Make sure the edges are nice and thin, but be careful not to press too hard so that the filling does not spill out of the sides. Making the Pupusas — Method 2:Divide the dough into 24 equal small balls. Divide the filling equally for the 12 pupusas. With wet hands, press and pat each ball between your palms and flatten into thin dough rounds that are about 4 inches in diameter and ⅛-inch thick. Place the flattened rounds on top of plastic wrap, waxed paper, or a damp kitchen towel to prevent them from sticking to any solid surface. With your fingers or the back of a tablespoon spread the cheese filling evenly on the 12 flattened rounds. Cover these with the other 12 flattened rounds and seal the edges with your fingertips taking care that the edges are nice and thin. Cooking the Pupusas:Heat a non-stick griddle or large heavy skillet over a medium to high flame. Typically, once the pupusas are formed by hand, using either method, they are placed straight onto the skillet or griddle. If you set them aside before cooking, make sure to wet your hands and gently pick up each pupusa, and pat lightly between the palms of your hands. Gently place the pupusas on the hot surface and cook for about 5 minutes on each side, frequently turning them over to ensure even cooking. The pupusas are ready when they puff up and turn slightly golden. Serve with Curtido.