Using a whisk or fork, mix flour, cream of tartar, xanthan gum and baking soda together in a small separate bowl.
Using your stand mixer (or handled mixer) cream the butter and sugar. 30 seconds to 1 minute.
Add the eggs and vanilla to the mixer. Mix throughly.
Add the dry ingredients from the separate bowl. Mix on low, be careful to not over mix. This will create dense yucky cookies.
If the dough is too tacky and doesn't scoop well, put the dough in the fridge for 30 minutes to an hour. Be careful not to over chill the dough because then it will be too hard to scoop. I usually don't need to chill the dough honestly.
Preheat over to 400°
Line your cookie sheet with parchment paper. Using a #40 cookie scooper (or smaller if you prefer) scoop the cookies out onto the sheet. Place equally apart so they cook evenly.
Using a fork, gently flatten the cookies.
Now I love soft cookies and I HATE hard cookies. So I will always undercook a cookie instead of accidentally over cooking them. I start with 7 minutes--keep an eye on the first batch to see how they go. Once they cool they will form up and be perfect. If your oven doesn't run as hot add on 30 sec or 1 minute and that should be good.