Mix corn flour and warm water to knead dough. Keep it aside for 10 minutes. Make into smooth balls with the palms of your hands.
Keep remaining dough covered with a damp cloth to prevent drying.
Open tortilla press and lay a plastic sandwich bag on the bottom half. Place ball of dough on the plastic, a little off-center, towards the hinge of the press.
Place another sandwich bag on top of the ball and flatten slightly with your hand. Close the press firmly, and then open.
Transfer the tortilla, dough side down, to your dampened hand. With free hand, carefully peel the bag off the dough.
Put it on the preheated griddle and roast it.
Note: Place the tortilla on the hot griddle and cook turning only once, like a pancake. This should take about 2 minutes.