Preheat the oven to 375 degrees F and place one rack in the upper third and the other rack in the lower third of the oven. Line two large sheet pans with parchment paper. I like to trace 3, 6-inch circles on each parchment, so my shells are the same size. (Flip the parchment over so you don't get pencil or pen on the cheese.)
Measure 1/3 cup (1 1/2 ounces) of shredded cheese per circle and spread evenly to the edges of the circle.
Bake for 5 minutes and swap the positions of the baking sheets. Bake another 5-10 minutes or until little holes have appeared in the surface of the cheese and the edges begin to brown.
Remove from the oven and blot with a paper towel before removing to wooden spoons or spatulas suspended by glasses to shape taco shells. (I now use a taco shaper which I have linked to in the post and it is much easier to shape the shells.) Leave on the pans to cool flat for chalupa or tostada shells.
Cool completely and store in an air-tight container on the counter for a few days or in the refrigerator for up to two weeks.
* Make sure to use ONLY pre-shredded cheddar cheese from a bag like Kraft brand. This never sticks to the parchment. I tried a mixed blend of Mexican cheese and it stuck a little and didn't get crispy. ALSO, if the cheese isn't cooked enough, it will stick. Make sure it starts to turn evenly browned - not dark, but not bright orange any more.
1 carb per shell.
To make a single serve cheese taco shell in the microwave, spread 1/3 cup of cheddar cheese into a circle (see photos in post) and microwave for approximately 2 minutes. This will take more or less time depending on the strength of your microwave. My microwave is not very strong.