Place the masa harina or cornmeal and a good pinch of salt in a bowl and mix together. Add half the measurement water and leave to stand for 10 minutes. Pour in the remaining water and the oil and mix together to form a soft, smooth dough.
Divide the dough into 10 equal pieces and roll each into a ball. Cover both sides of a tortilla press with clingfilm. Place a ball of dough inside and press down to flatten. Alternatively, place a ball inside a large plastic food bag and either roll out on a work surface or use a heavy-based saucepan to flatten the dough into a round about 1–2 mm (⅛ inch) thick. Repeat with the remaining dough.
Heat a large, dry nonstick frying pan until hot. Peel away the clingfilm from the tortillas, place 1 in the pan and cook for 1 minute on each side until lightly charred. Repeat with the remaining tortillas. Serve with fajitas, fried as chips (see below) or with guacamole (see