Preheat your oven to 350 degrees f and line a cookie sheet with parchment paper
In the bowl of your stand mixer fitted with a paddle attachment, add your softened butter and white sugar. Beat on high speed until creamy and paler in color
To the butter mixture, add the vanilla extract and egg and mix on medium speed until well incorporated
Turn the mixer off, and, to the wet ingredients, add the flour, baking soda, cream of tartar and salt. Start on low speed and gently incorporate them.
Once the flour is JUST combined, turn the mixer off and remove the bowl
Use a rubber spatula to gently fold the chocolate chips in, then use a cookie scoop to portion out the cookies into 2 tablespoon sizes
Roll the portioned dough into balls and place each one 2 inches apart on your prepared baking sheet and top with extra chocolate chips if desired
Bake in the preheated oven for 9-10 minutes, until the edges are lightly golden brown. Take the baking sheet out of the oven and let the cookies cool for 4-5 minutes
Use a flat rubber spatula to transfer the baked cookies to a wire rack to finish cooling, and follow directions 7-9 for the remaining cookie dough balls
Notes
Use room temperature butter
Really cream the butter and sugar until light and paler in color
If you don't have a stand mixer, an electric hand mixer will work
Don't overmix the dough once the dry ingredients are added or else your cookies will be dense and tough
Fold the chocolate chips in by hand so they don't break
Make the cookie dough the night before to save time. Just let the dough come to room temp before baking
Bake for 12-13 minutes if you like a crispy cookie
Store leftover cookies in an airtight container on the counter for 3-4 days