In a large bowl, whisk together the flour, cream of tartar, baking soda, cinnamon and salt; set aside.
In a small bowl, whisk together the eggs and milk; set aside.
In a medium saucepan set over medium heat, melt the butter until the foam subsides and the butter turns nut brown, 8 to 10 minutes, swirling the pan occasionally.
Pour the browned butter through a strainer into the bowl of a stand mixer fitted with the paddle attachment. Beat butter on medium speed until it cools to room temperature, 5 to 7 minutes.
Add granulated sugar and brown sugar and beat on medium speed for 2 minutes. Scrape down the sides and bottom of the bowl and beat again for a few seconds.
Turn the mixer to low speed and add the egg mixture. Mix until combined. Slowly add the flour mixture and mix until just barely incorporated, scraping down the sides of the bowl as needed.
Gather the dough into a mound in the middle. Cover the bowl and chill in the refrigerator for at least one hour.
Preheat the oven to 400 degrees F. Line two baking sheets with parchment paper.
In a medium bowl, stir together sugar and cinnamon for cinnamon sugar coating.
Using a cookie scoop or spoon, scoop about 2 tablespoons of dough and form a ball. Roll the ball in the cinnamon sugar mixture. Repeat with remaining dough. Place the cookies on baking sheet and bake for 10 minutes until cookies are slightly cracked.
STORAGE: Store these cookies in a sealed container for up to 3 days.FREEZING: You can freeze the dough before baking, with or without the cinnamon sugar coating. We recommend freezing the balls without the coating. When you are ready to bake, remove them from the freezer. Let them sit for 30 minutes at room temperature, then roll in the cinnamon-sugar coating and bake. SUBSTITUTIONS:
All Purpose Flour: You can substitute with 1-1 gluten free all purpose flour, if desired.
Light Brown Sugar: Darn brown sugar is not recommended as it alters to flavor of these cookies.
Cream of Tartar: This helps give the cookies the signature snickerdoodle texture and flavor. You can substitute the cream of tarter AND the baking soda with 2 teaspoons of baking powder, but the cookies may not have the traditional snickerdoodle flavor.