Preheat the oven to 350 degrees F. Line two baking sheets with parchment paper and set them aside.
In a medium-sized bowl, whisk together the all-purpose flour and graham cracker crumbs. Set this aside.
Add the egg, vanilla extract, Key lime juice, lime zest, salt, and baking soda. Beat for another minute, scraping down the sides of the bowl as needed.
Bit by bit, add the dry ingredients to the butter and sugar mixture. Mix until everything just comes together.
Scoop the dough onto the prepared baking sheets (in ~1-inch balls), approximately 2 inches apart from one another. Bake for 9-10 minutes, or until the edges are lightly golden.
Once the cookies have cooled completely, dust the cookies with powdered sugar and a bit of extra lime zest.