Place the masa ball in between the two sheets of the plastic bag. Press inside a tortilla press or place on a strong flat surface and roll out to a thin circle. Carefully lift the top layer of plastic off and place the masa side down on your hand while again carefully peeling back the remaining plastic.
Add masa harina, baking powder and a big pinch of salt in a mixing bowl, slowly add the warm water as you churn the mixture with your hand or a mixing spoon. Continue to churn the mixture and add more warm water until the consistency of the mix is soft but not too wet. To touch, the masa shouldn’t stick to your hands, but should leave an imprint.