Beat the butter and sugar until light and fluffy, scraping the bowl as needed, for about 3 minutes.
Meanwhile, whisk together the flour, salt, and cream of tartar in a medium mixing bowl. Set aside.
Add the egg and vanilla and beat until combined.
Turn the mixer to low and add in the flour mixture, until just combined.
Press the mixture evenly into the prepared pan filling each section to the top.
Bake for 10 -12 minutes (depending on the method you use) until the cookies are lightly golden.
Cool 5 minutes before carefully lifting the cookies out of the pan and transfering to a cooling rack to cool completely.
Notes
Beating the butter and sugar together really well is an important step as it ensures the cookie is light, crisp, and holds together.
Make sure you pack the dough and fill the cavity to the top to ensure a flat bottomed cookie. If you need to, use a knife to flatten them off before icing.
A #16 cookie scoop is the perfect size for measuring the mixture. Alternatively, you can use a 1/4 cup measuring cup.
For a spiced variation, add ground ginger, nutmeg, or cinnamon to your dough. Experiment with flavors.
These cookies are perfect for icing and decorating, they taste amazing with a simple glaze and a few sprinkles. Make them your own.