Heat a cast iron skillet or a comal over medium heat. Prepare a clean kitchen towel to wrap tortillas to keep them warm and cut 2 plastic sheets about 10x10-inch (25×25 cm) each.
In a medium bowl add masa-harina and start adding water while mixing with your hands until combined.
Knead for a minute or two, adding a little more water if needed, until a no-stick and soft dough forms.
Divide the dough into 8 equal portions. Form balls and cover them with a damp kitchen towel to prevent dough from drying.
Place one of the balls onto one of the sheets and press it a bit with your fingers to make a patty.
Cover with the other plastic sheet and then place over a heavy baking dish pressing firmly to shape a 6-inch (15cm) round tortilla.
Gently remove the plastic on each side of the tortilla, placing it carefully on your hand.
Lay the raw tortilla on the hot skillet/comal and cook for about 40-45 seconds, then flip it up and cook for another 45 seconds.
Turn the blue tortilla over again and cook for another 15 seconds, until it begins to puff.
Place the blue corn tortilla between a kitchen towel to keep it warm. Repeat the steps with the remaining dough.
If you having troubles to lay the tortilla on the skillet for cooking, wet your hands a little bit so it won't stick to your fingers.
For perfect blue corn tortillas, you need to find a balance between too much water and too little. This can only be achieved after trying the recipe multiple times as the texture of masa varies depending how much humidity is in the room.
A perfect masa (dough) should be moist enough to result in soft tortillas but at the same time, not too wet that you can't handle it. And not too dry that it will crumb.
Masa dough will let you know when it needs more or less water, so "listen to her".
If the tortilla doesn’t puff while cooking means you need to cook the tortilla a little more longer. Also, you can press a little bit with your hands (carefully) or with a spatula to make it puff.