Preheat the oven to 350°F (177°C). Arrange oven-safe bowls upside down on a baking sheet to use as molds and have a ladle or small bowl ready for shaping.
Heat 2 tablespoons oil in a large skillet over medium heat until hot (about 350°F on a thermometer) but not smoking.
Add one tortilla to the hot oil and fry 30–45 seconds on the first side until golden in spots, then flip and fry the second side 30–45 seconds until the tortilla is deep golden and begins to puff.
Use tongs to immediately lift the tortilla from the skillet and drape it over an oven-safe bowl; press gently with a ladle or small bowl to shape it into a shell. Sprinkle with kosher salt if desired.
Repeat frying and shaping with the remaining tortillas, adding more oil to the skillet as needed to maintain the frying temperature.
Place the shaped tortilla shells (on their bowls) on the baking sheet and bake at 350°F (177°C) for 12–14 minutes, or until crisp and golden brown.
Remove shells from the oven, lift them off the molds, and cool on a wire rack before serving.
