A freshly-made taco shell usually beats the dry shop-bought varieties hands down for both taste and texture. You can make your own taco shells at home in just five to 10 minutes, so why not make the shells while your taco meat is cooking.
Add vegetable oil to a pot or frying pan until there is about 2.5 cm (1 inch) of oil. Heat the oil up to about 120 degrees C (250F).
Place one tortilla into the oil, making sure it is completely submerged momentarily. The tortilla will float to the top of the oil once it begins frying.
Use a fork to hold the bottom half of the shell down in the oil and use another fork to fold the tortilla in half. Hold the top half away from the bottom half and allow the shape to set as it cooks.
Turn the shell over in the oil after about 30 to 60 seconds. The half of the shell that was out of the oil is now submerged and the part that was in the oil is now out of it. Continue to use the forks to hold the shape of the shell as well as to hold the bottom half under the oil.
Test if the shell is done after another 30 to 60 seconds has passed. If it has not hardened yet, continue to hold each half of the shell under the oil for as long as it takes to become crispy. Turn the shell so that each half gets equal time in the oil. (Or else one half will be crispy and the other soggy!)
Remove the shell from the oil and place it onto a plate or pan covered in paper towels. This will drain the shell of excess oil and allow it to set to its final crispiness.
Repeat these steps for as many shells as you wish to make.
You may want to test the oil with a piece of tortilla first. Use oil that is too cool and you will end up with soggy tortillas that are not cooked. Oil that is too hot will cause the tortillas to "balloon" due to the moisture inside. Finding the right temperature to cook the tortillas at will take some trial and error.
Keep in mind that the shell will continue to harden after it is taken out of the oil. Shells that become too crisp while in the oil may shatter when you try to bite into them.
Working around hot cooking oil is dangerous and hot oil should always be handled with care.