Preheat oven to 375 degrees.
Line several baking sheets with parchment & set aside.
In a medium-sized bowl, combine flour, cream of tartar, baking soda, cinnamon & salt. Set aside.
In a large bowl, cream butter & sugar together.
Add egg and egg yolk and vanilla & mix until just combined.
Add the dry ingredient mixture to the butter mixture slowly and beat until a creamy dough forms.
Fold in white chocolate chips - if using.
Whisk together coating ingredients in a small bowl.
Shape dough into balls & roll in the cinnamon/sugar mixture.
Place on the prepared baking sheet about 2 inches apart.
Add a couple more chocolate chips to the tops of the dough if using.
Bake 10-12 minutes. Cookies will be puffy and soft, but will flatten as they cool. Cool on wire rack at least 20 minutes before transferring to an airtight container.
If adding the glaze, wait until cookies are completely cooled before doing so.
Once cooled, whisk together glaze ingredients & dip cookies into the mixture.
Place on parchment paper to dry before serving.