Actually, the flour (or harina) used in tortilla and a number of other "corn" based doughs is not just cornflour. That would imply that it is just dried corn, ground to a flour. The flour in tortilla and many other, but not all, corn doughs used in Latin American cuisines is masa harina. For this, the corn is first put through a process called nixtamalization. The corn is cooked with lime (chemical lime not the fruit), or other alkaline solution (sometimes wood ash). The husk is removed from the kernel then it is dried before being ground. It actually makes the corn more nutritious, but in the process changes the flavor significantly, so they are not, technically the same, and won't give you the same end product.