n a large bowl, beat together the butter and sugar until fluffy. Then add in the egg and vanilla and beat until combined.
In a small bowl, whisk together the flour, baking soda, salt, and cream of tartar.
Add half of the flour mixture to the wet mixture, fold until completely incorporated, then add in the rest of the flour mixture and fold again until incorporated. (it will seem a little dry, but it will come together once you start pressing it with your hands)
Press the dough into a round disc and refrigerate for 15 minutes. (I just leave it in the same bowl)
Once cooled, press the dough onto a pizza pan. Start in the center and just use two hands to press the dough outward until you have about a 9-inch circle that's about ¼-inch thick. (You do not want to get all the way to the edges of your pan because the dough will spread in the oven)
Bake the dough for 10-12 minutes or until you see the edges just start to turn golden. When it's done, remove from the oven and let it cool on the pan completely.
Making the Icing:
Beat the cream cheese, vanilla, and lemon juice until smooth.
Sift in the powdered sugar then fold in with a spatula until combined. Spread evenly over the cooled cookie crust.