There is a recipe I have that makes lemon pistachio shortbread cookies, but the price of purchasing dehydrated lemon peel is pretty scary, so I learned how to do it myself. It is a time consuming process, but worth the effort.
First, you take a clean lemon and you begin to peel the skin off of it with a knife, trying to get as little of the bitter white part as possible.
Second, you lay the lemon peel on a plate, cover with a towel if you like (suggested for keeping bugs and pet hair off), but you won't want to cover it with plastic wrap or foil, you want the peel to be able to breathe.
Third, let it air dry on your counter top for about 4 days
Fourth, take the small grates on a cheese grater, and begin to grate the lemon peel.
Fifth, store in an airtight container.
You can also do this with pretty much any citrus fruit! I plan on grating it first next time I decide to do this. I usually grate the part that has the hole where it was attached to the tree, or the part of the lemon just opposite of that, while it is still on the fruit and not dried. I do that when I zest over meats or into salads, because the skin is thicker in those parts and makes it much easier to zest.
I hope you find this information useful, thanks for reading!