Weigh out the flour in a large bowl. Add the baking soda, salt, baking powder and cream of tartar. Stir for at least 60 seconds to make sure all dry ingredients are evenly mixed.

In the bowl of a stand mixer with the paddle attached, beat the cold butter until soft. Add both sugars and continue to beat for 4 minutes, scraping sides of bowl, until fluffy and light. Beat in the vanilla extract.

Stir in the egg using lowest speed (or by hand) and then increase speed and beat for 30 seconds. Scrape bowl and then gradually add flour mixture, stirring either by hand or using quick pulses of the stand mixer (I use a combination of both in order not to overbeat the dough). Add the chocolate chips and stir until blended. Dough will be very dry. I recommend dumping it out onto a pastry mat (or clean surface) and kneading gently to ensure it is thoroughly mixed.

Shape into one big mound, then divide into 12 equal size balls (they’ll weigh a little under 3 oz each). Put the dough balls in a freezer bag and chill until ready to bake, or bake immediately.

Bake in a preheated 375 degree oven for about 15 minutes. If your cookies are browning too quickly (and they shouldn’t) you can use 350 degrees, but since the cream of tartar impedes browning a little bit they should be fine baked at 375.