Add egg, lemon juice, zest, and vanilla, and mix to combine.
Add in the dry ingredients and mix well.
Refrigerate for one hour.
Roll balls (dough will be sticky), roll in powdered sugar and bake on cookie sheets lined with parchment paper. Bake for 12-15 minutes in a 350º oven. Let cool for a minute or two before transferring to a cooling rack.
The lemon essential oil or extract is optional, but I love to add lemon essential oil to make the lemon really stand out!