In a mixing bowl, whisk together all-purpose flour, baking soda, cream of tartar, and salt.
In another bowl, beat together butter, white sugar, and brown sugar until light and fluffy, about 2 to 3 minutes, using a hand beater or stand mixer fitted with the paddle attachment. Scrape down the sides of the bowl as needed. Then add the eggs and vanilla extract, and beat again until fully incorporated.
Add the dry ingredients to the wet ingredients and beat together just until a dough forms. The dough will be soft and fluffy.
On a large piece of parchment paper lightly dusted with flour, roll out the dough into a rectangle.
In a small bowl, make the cinnamon sugar spread by combining softened unsalted butter, dark brown sugar, and cinnamon. Spread this mixture evenly on top of the dough.
Roll the dough tightly into a log. If it feels too sticky, sprinkle a little more flour. It’s okay if it’s not perfectly shaped. Wrap the dough using the parchment paper and place it in the freezer to chill for 20 to 25 minutes.
Slice the chilled dough log into 1-inch thick pieces and freeze for about 30 minutes.
Preheat your oven to 375°F.
Arrange 6 cookie slices on a lined baking sheet, making sure they are spaced apart.
Bake for about 12 to 14 minutes, until the edges turn golden brown.
Remove from the oven and allow the cookies to cool on the baking sheet until they are movable. Then transfer them to a cooling rack to finish cooling.
To make the vanilla glaze, whisk together powdered sugar, heavy cream, and vanilla extract. If the glaze is too thick, microwave it for 15 seconds to thin it out.
Spread the glaze over the top of each cookie. Once the glaze sets, your cookies are ready to enjoy!