In a large mixing bowl, use a hand mixer to cream together the softened butter, granulated sugar, and brown sugar until light and fluffy for about 1-2 minutes.

Add the two room temperature eggs and vanilla extract to the mixture, beating on medium speed until fully combined, approximately 1 minute.

In a separate bowl, whisk together the all-purpose flour, cream of tartar, baking soda, cinnamon, and salt, then gradually add this dry mix to the wet mixture.

Cover the dough with plastic wrap and refrigerate for at least 1 hour, or up to 24 hours for optimum flavor and texture.

Preheat your oven to 350°F (175°C) and line your baking sheets with parchment paper.

Once the dough is chilled, scoop about 1.5 tablespoons of dough and roll into balls, then roll in a mixture of cinnamon and sugar or colorful sprinkles.

Bake the cookie dough in the preheated oven for 10-12 minutes, or until the edges are lightly golden.

Remove the baking sheets from the oven and let the cookies cool for a few minutes before transferring them to wire racks.