Howdy, I baked a few dozen corn tortillas yesterday morning. This was about my third try, and they were very consistent in quality. They're mighty tasty, the way fresh corn tortillas are supposed to be, which is virtually nothing like what you buy in the store. Here's how to do it.
Go to the Mexican food section of your grocery store, or to a Mexican store, and buy Masa Harina. This is corn that has been wet-ground with lime, and then dehydrated to a flour-like consistency. Nothing else will do. I bought a five-pound sack a couple of weeks ago for around $3.50.
Put a cup or two into a bowl. Add hot tap water and stir until it takes on a texture like chocolate chip cookie dough (without the lumps, of course). If it is too dry, your tortillas will be very heavy and stiff. If it is too wet, they will be fragile and difficult to handle, and they won't cook properly.
Now let your dough sit for around 15 minutes, which should give you enough time to heat your well-seasoned or non-stick griddle to HIGH. I've tried various temperatures, and HIGH is the only one that works for me. Set up your tortilla press, using plastic freezer bags cut into sheets somewhat bigger than the press.
When the dough is ready and the griddle is hot, roll a ping-pong-ball-sized wad of dough into a ball, place it on the press between two sheets of plastic and press lightly. Open the press, turn it 180 degrees and press again, somewhat harder, so it is nearly the size of the press. Open the press and peel the plastic off the top of the tortilla. Turn the tortilla onto the palm of your right hand so that one edge is even with the outer edge of your index finger on your right hand, and starting at that edge, carefully peel the second sheet of plastic off the tortilla. There will be a good bit of tortilla hanging off the outer edge of your little finger.
Sweep your hand above the hot griddle and turn it slightly so that the tortilla is laid smoothly onto the griddle. At first the tortilla will stick to the griddle. As soon as it will slide freely (this takes 5 or 10 seconds), use your fingers to pick it off the griddle and flip it. I slide mine to the edge, grab the edge and flip. Let it sit a few more seconds, then flip again. After the second or third flip, bubbles will start to form in the tortilla. Wad up a smooth cloth (t-shirt, flour sack dish cloth, etc.) so you have a wad with a smooth surface, and press that gently onto the tortilla. This will encourage the steam to form bubbles, which will increase in size. You can push on the bubbles lightly to get them to grow larger. Keep pushing and flipping the tortilla until eventually the whole tortilla puffs up like a little pillow. Let it cook a bit like this, until there are golden brown spots, then pick it off the griddle. Stack the hot tortillas under a slightly damp towel.
So there it is. I imagine you could add tomatoes that were ground up very fine if you wanted. I think flour tortillas are done about the same, except with a much larger press. Good luck!