In the bowl of a stand mixer {fitted with paddle attachment} combine butter, sugar, eggs and vanilla extract. Beat on medium speed until creamed {it should be light and fluffy}. This will take between 4-5 minutes but do not skip this part. Scrape down sides of bowl as necessary.
Add flour, cornstarch, cream of tartar, baking soda and salt and mix until just combined. In a separate small bowl combine Cinnamon Sugar Coating ingredients and mix well.
Using a medium cookie scoop {or 2-3 tablespoons of dough} form mounds. Roll each mound in the Cinnamon Sugar Coating and place on a pan lined with parchment or wax paper. Cover with plastic wrap and refrigerate for at least 2 hours and up to 5 days.
When ready to bake, preheat oven to 350 degrees. Line cookie sheets with parchment paper or spray with cooking spray. Place mounds on sheets, being sure to space them about 2 inches apart. Bake for 8-9 minutes, or until the edges are set and the middle of the cookie is just beginning to set. They will look under baked but let them cool on cookie sheet for 5-7 minutes before moving to a cooling rack and they will firm up as they cool.
Store cookie in an airtight container at room temperature for up to a week or freeze for up to 3 months.