Make the cookies: In a medium bowl, whisk together flour, cream of tartar, baking soda, and salt. Set aside.
In a mixer bowl fitted with the paddle attachment, beat butter and sugars on medium speed until light and fluffy, about 3 minutes. Add eggs, one at a time, beating well after each addition. Beat in vanilla extract. Add flour mixture and beat on low speed just until combined. Do not overmix.
If the dough is soft at this point, chill in the fridge for at least 1 hour, or overnight. This step also results in thicker cookies that will spread less while baking, but it's not mandatory.
Preheat oven to 350F/180C. Line 2 pans with parchment paper. Set aside.
Make the coating mixture: In a small bowl, toss together all the ingredients.
Shape the dough into balls, the size of 1.5 tablespoons each. Roll them in the coating mixture, and place on the cookie sheets. Bake for 10-11 minutes until cookies just begin to brown at the edges but the center is still soft. Allow cookies to cool on baking sheet for 5-10 minutes, then gently transfer to a wire rack to cool completely.
Store cookies at room temperature in an airtight container for up to 3-4 days. Cookies can also be frozen for up to 2 months.