2 1/2 cups (10 ounces) masa harina
1 teaspoon salt
1 2/3 cups warm water
2 quarts vegetable oil
Mix masa harina and salt together in medium bowl. Stir in warm water with rubber spatula.
Using your hands, knead mixture in bowl until it comes together fully (dough should be soft and tacky, not sticky), about 30 seconds.
Cover dough with damp dish towel and let rest for 5 minutes.
Divide dough into 12 equal portions, about 1/4 cup each, then roll each into smooth ball between your hands. Transfer to plate and keep covered with damp dish towel. Cut sides of 1-gallon zipper-lock bag, leaving bottom seam intact.
Set wire rack in rimmed baking sheet and line rack with triple layer of paper towels. Add oil to large saucepan until it measures 2 1/2 inches deep and heat over medium-high heat to 375 degrees.
When oil comes to temperature, enclose 1 dough ball at a time in split bag. Using clear pie plate (so you can see size of tortilla), press dough flat into 6-inch circle (about 1/8 inch thick).
Carefully remove tortilla from plastic and drop into hot oil. Fry tortilla until it puffs up, 15 to 20 seconds. Using 2 metal spatulas, carefully flip tortilla. Immediately press down in center of tortilla with 1 spatula to form taco shape, submerging tortilla into oil while doing so. Using second spatula, spread top of tortilla open about 1 1/2 inches. Fry until golden brown, about 60 seconds. Adjust burner, if necessary, to maintain oil temperature between 350 and 375 degrees.
Transfer taco shell to prepared rack and place upside down to drain. Return oil to 375 degrees and repeat with remaining dough balls.