In a stand mixer or with a handheld electric mixer, cream together the butter, sugar, and lemon zest. Mix for 3-4 minutes or until the mixture is lighter in color and fluffy in texture.
Using a handheld spatula or whisk, gently mix the egg, lemon juice, and vanilla into the butter mixture until fully combined.
In a separate bowl, mix together the dry ingredients. Add the flour, baking powder, salt, baking soda, and cream of tartar. Use a fork and mix until the ingredients are evenly distributed.
Add the dry ingredients to the butter mixture. Using a spatula, fold the flour mixture into the wet ingredient until JUST combined. Do not overmix the dough.
Using a cookie scoop or a spoon (each cookie needs to be about 2 ish TBSP's), scoop the dough into individual balls and place on a plate.
Shape each piece of dough into a ball and roll in the lemon sugar mixture until fully covered.
Place dough onto a parchement lined cookie sheet (only bake 8 per sheet to prevent them from sticking to each other). Very lightly press down on each dough ball with your hand to flatten it a bit.
Bake for 9-11 minutes or until the edges BARELY start to turn golden. Do not over-bake these cookies. If anything, pull them a bit before you think they are done because they will continue to cook on the pan.
Cool the cookies completely and store at room-temperature for 2-3 days for maximum freshness.