Preheat the oven to 350°F (180°C) and remove the oven grids.
Microwave the tortillas for 15-30 seconds until they are soft and pliable. Alternatively, heat them in a pan over medium heat until warm and soft.
Spray the tortillas with cooking spray or brush them with avocado oil. Optionally rub them with chili powder or your favorite spice mix.
Drape each tortilla over 2 bars of your oven rack and pinch the bottom to help them hold that U-shape.
Bake the tortillas on the middle rack of your oven for 8-10 minutes until golden brown. Don't worry if the ends don't bow right away, they will over time. Place aluminum foil or parchment paper underneath the tortillas to catch the oil that drips down.
Remove the tortillas from the oven with cooking tongs and let them cool and a cooling rack.
Notes
Don't use wheat tortillas, as they won't get as crispy as corn tortillas.
You can store the taco shells in an airtight container on your kitchen counter for 2-3 days. However, baked taco shells always taste best fresh and can become a little stale over time.
To reheat the taco shells, place them in a baking dish or onto your oven rack and reheat them at 300°C (150°) for 10-12 minutes. Do not reheat them in the microwave.