Preheat oven to 350 degrees F. Line 2 cookie sheets with parchment paper.

In a small bowl, add in the butter, brown sugar, and cinnamon. Using a spatula, work the butter into the cinnamon and brown sugar until the filling comes together. Set aside.

In a medium bowl, add the flour, baking soda, cream of tartar, and salt. Whisk until combined.

In a large mixing bowl, add the butter and granulated sugar. Beat with a hand mixer on medium speed until light and fluffy, about 1 to 2 minutes.

Add the egg and vanilla extract. Beat until the egg is incorporated.

Stir in the dry ingredients into the wet ingredients until just combined.

Using a 1 tablespoon cookie scoop or a 1 tablespoon measuring spoon, scoop out the dough balls and make an indentation in the center using your thumb or the end of the spoon.

Fill each indentation with a scoop of the filling mixture and seal the ball up around it. It’s okay if some of the filling shows through; just make sure you arrange cookies filling-side-up on a cookie sheet.

Once all of the dough balls are filled, work on the coating.

In a small bowl, add the 3 tablespoons of granulated sugar and 1 teaspoon of cinnamon. Stir until combined.

Roll each dough ball in the cinnamon sugar until completely coated.

Arrange the dough balls about 2 inches apart on the prepared cookie sheets and bake for 12 minutes or until the cookies are set around the edges.

Remove the cookies from the oven and let cool for 5 minutes before transferring to a wire rack to cool completely.