Pour vegetable oil into a heavy-based frying pan or deep saucepan to a depth of about 3 cm.
Heat over medium-high heat until the oil reaches 175°C or until a small piece of tortilla sizzles and floats immediately.
Working one at a time, carefully slide a corn tortilla into the hot oil and fry for 10-15 seconds on each side until it’s soft and pliable.
Using tongs, fold the warmed tortilla in half and hold it in place, frying for 30-60 seconds on each side until golden and crisp.
Transfer the shell to kitchen paper to drain and, while still warm, sprinkle both sides with salt.
Repeat with the remaining tortillas.
Allow the shells to cool briefly, then fill and serve immediately, or store cooled shells in an airtight container at room temperature for up to two days.