Combine the flour, baking powder, and salt using your hands or a pastry cutter and crumble or cut in the shortening until the mixture is crumbly. If it looks more powdery than crumbly add a tablespoon or more shortening until it is crumbly.
Add just enough of the HOT water to make the ingredients look moist.
Now, knead the mixture. Kneading anywhere you see any loose pieces or flour so you are sure to get everything. If it sticks to the anything add a some more flour. Play with the dough and the flour and shortening amounts until you have a dough that makes a soft round shape. You want your dough to be smooth and sort of elastic.
Cover bowl with a towel and let it rest for about an hour.
After it rests, cut or pinch off 10 to 12 balls. Add some flour to your rolling pin and workspace LIGHTLY. Roll each ball into about 1/8 inch thickness or press with a tortilla press that has plastic wrap covering any part that the dough will touch.
Cook tortilla's one at a time on a medium hot cast iron skillet or griddle for about 1 to 2 minutes on each side, or until the tortilla gets brown specks. Black specks mean your pan is too hot. Reduce heat so the tortilla puffs and browns. It should puff up underneath if done right. Do not worry if it does not though. Practice will get you to that stage.
NOTE: Here are some tips as to technique: Do not use bread flour. You want flour with a low gluten content. You don't want to over-flour your work surface, but you don't want your rolled-out tortilla sticking to it either. I found that the dough adhered less to an unvarnished wood surface (like an old cutting board) than any other surface I tried. A flat dough scraper, or "bench knife" is perfect for removing the rolled-out tortilla from the work surface. When rolling out tortillas, dust your rolling pin with flour, and don't be afraid to apply some pressure. Flour tortilla dough is pretty sturdy; but not to the point of rerolling. You don't want tough tortillas. Making perfect circles is harder than it sounds; the dough wants to draw up. So if perfectly circular shapes are important, you can trim away the excess with a sharp knife.