Using a stand mixer with the paddle attachment or an electric hand mixer and large mixing bowl, cream together softened butter and both sugars on high speed for 2 minutes.
Add the egg, egg yolk and vanilla. Continue mixing for a 2 more minutes.
Meanwhile, to a separate bowl, add the flour, cream of tartar, baking soda, nutmeg, and cinnamon. Whisk well, to combine.
With the mixer running on low speed, slowly add the flour mixture to the wet ingredients. When ingredients are just combined, turn off the mixer.
Cover the bowl of dough and refrigerate for about 1 hour.
When ready to bake, line two cookie sheets with parchment paper. and preheat the oven to 375°F.
In a small shallow bowl or on a plate, mix the sugar and cinnamon topping ingredients.
Using a cookie scoop or a small spoon, scoop about 2 Tablespoons of cookie dough. Form the dough into a ball shape, then roll through the cinnamon sugar mixture.
Arrange balls of dough about 3 inches apart on prepared cookie sheets. Bake in preheated oven for approximately 8-10 minutes.
Remove pans from oven. Allow snickerdoodles to cool on the cookie sheet for 5 minutes, then transfer to a wire rack to cool completely.
Notes
Storage - Snickerdoodle cookies will stay fresh in a cookie jar (or another airtight container) at room temperature for two to three weeks. You can make the cookie dough ahead of time and freeze it to make it at another time. Store the cookie dough in suitable freezer-safe container for up to 3 months.
Thicker cookies - Refrigerating the dough before baking the cookies prevents them from spreading too much in the oven.