Take butter and eggs out of the fridge at least 60 minutes before you're ready to bake to soften butter and bring eggs to room temperature (or, see recipe notes).
Pre-heat oven to 400 degrees.
In a medium sized bowl, mix flour with cream of tartar, baking soda, chai spice, (and salt if using unsalted butter), and whisk so that it is all well combined.
In a small bowl, mix the sugar coating and set aside.
In a large bowl, add softened butter and sugar. Use a hand mixer (or a stand mixer with the paddle attachment) on low speed and mix butter and sugar together until just combined, about 1-2 minutes.
Add one egg at a time, mix in with butter and sugar until just combined, then add second egg. Beat/mix until eggs are just incorporated, do not overbeat. Only about 15-30 seconds for each egg.
Slowly add flour mixture to creamed butter, sugar, and eggs, about 1/3 of the mixture at a time. Use a spatula to scrape the butter and sugar off of the edges of the bowl and fold down into flour mixture and mix. Then use a large spoon to mix it all together before adding next 1/3 amount of the flour mixture until all flour is mixed into a dough.
Roll out 1-2 inch balls in the palm of your hand, or use a cookie scoop. Roll the ball in the sugar coating, ensuring it's all well coated.
Place coated cookie dough balls on an ungreased baking sheet 2 inches apart.
Bake in middle rack for 9 minutes.
Let cool on baking sheet for 5 minutes before transferring to a wire rack.
Store in an airtight container for up to a week.