These ingredients and instructions are for one roti. Therefore, if you want to make 10 roti, you will need 10 bananas, 10 eggs...etc. However, I would recommend only cooking one roti at a time.
1 or 2 hours before cooking the roti, pull the dough balls from the refrigerator and allow them to come to room temperature while still covered in plastic wrap.
In a small bowl, beat one egg lightly.
Cut the banana into thin slices and gently mix it with the beaten egg
Add a thin layer of oil to the pan and heat it slowly over low or medium low heat as you stretch the dough. The trick is to have the pan hot when you are done stretching the dough
Oil a roughly 15 x 15 inch section of clean countertop with cooking oil. Make sure the counter is flat and smooth. Place one dough ball in the center of this oiled area. If the dough ball has become misshapen, try to form it back into a ball at this point.
Use the palm of your hand to gently flatten the ball.
The dough should feel very soft and give easily to the pressure of your hand.
Keep flattening the dough using the palm of your hand until it is roughly 4-5 inches in diameter. Try your best to keep the dough round as you flatten it.
Once the dough is in a roughly 4-5 inch circle, start to use your finger to press and stretch the dough against the counter. Try to keep the dough round and maintain an even thickness as you stretch.
Keep gently pressing and stretching the dough until it has reached a roughly 10-12 inch diameter. The dough should be quite thin at this point.
Turn the heat up to medium or medium-high and check the temperature of your pan, it should be hot and the oil should be shimmering but not so hot that the oil is smoking.
Carefully lift the dough off of the countertop.
Try to keep your fingers spread out as you lift the dough so that the sides of the dough don't fold over on themselves.
Move the dough over to the hot pan.
Lay the roti into the pan, trying to keep it from folding over on itself.
The roti should lay flat in the pan but if a few edges fold over on themselves, don't sweat it. It will still taste great. The roti should start to bubble slightly as soon as it hits the pan. let the roti cook for about 15-30 seconds, or until it looks like the dough has just cooked through.
Add the banana and egg mixture to the center of the roti.
Once you have added the banana/egg and the dough is set enough for you to fold it, use a spatula to fold one edge toward the center. Take note of how much browning is on the bottom of the roti at this point. If the roti is already browning heavily, turn down the heat.
Fold the opposite side over so that it meets the first fold in the middle.
fold one of the other sides toward the center.
fold the last side over so that it meets in the middle.
Flip the whole roti over and add the 1/2 tbsp butter to the pan. At this point you should be paying attention to how much color the roti is getting. Adjust the temperature so that the roti can brown and get crispy without burning.
Keep flipping and turning the roti in the pan so that it cooks in the butter and gets nice and crisp. Total cooking time after you add the butter should be somewhere around 2-3 minutes, but may vary a bit.
Once the roti is nicely golden and crisp, remove it from the pan and place it on a cutting board.
Cut the roti into squares. Six or nine pieces, your choice.
Place the warm roti on a plate and top with as much condensed milk as you like. Start the whole process over to cook more roti using the rest of the dough balls.