Line a baking sheet with paper towels and set nearby to drain and cool shells.
Pour oil into a medium–large skillet to a depth of about 1/4 inch and heat over medium until it reaches about 350°F on a thermometer or is hot but not smoking.
Carefully slide one tortilla into the hot oil and fry 12–15 seconds until golden and bubbly on the first side.
Flip the tortilla, then use tongs to immediately fold it in half and hold it folded while frying another 10–12 seconds per side, or until evenly golden brown.
Use tongs to transfer the fried shell to the prepared baking sheet; immediately sprinkle lightly with kosher salt and, if desired, open slightly and set upside-down to cool so they stay more open for filling.
Repeat frying and seasoning with the remaining tortillas until all shells are fried and cooled on the paper towels.
