Prepare the Filling: In a small bowl, combine the softened butter, brown sugar, and cinnamon. Mix until well combined and set aside.

Make the Dough: In a large mixing bowl, cream together the softened butter and granulated sugar until light and fluffy, about 3 minutes. Add the eggs and vanilla extract, and beat until smooth.

In a separate bowl, whisk together the flour, baking soda, kosher salt, and cream of tartar. Gradually add the dry ingredients to the wet ingredients, mixing until just combined.

Roll the Dough: Divide the dough in half and roll each half out between two sheets of parchment paper into a rectangle, about ¼-inch thick. Spread half of the cinnamon filling evenly over the dough, leaving a small border on all sides.

Roll Up the Dough: Starting from one edge, roll the dough tightly like a jelly roll. Once rolled, slice the dough into ½-inch thick pieces and set aside. Repeat with the second portion of dough.

Prepare the Cinnamon-Sugar Coating: In a small bowl, mix together the granulated sugar and cinnamon for the coating. Roll each cookie slice into the cinnamon-sugar mixture, coating both sides.

Bake the Cookies: Place the cookie slices on a parchment-lined baking sheet, spacing them about 2 inches apart. Bake at 350°F (175°C) for 10-12 minutes, or until the edges are lightly golden.

Cool and Serve: Allow the cookies to cool slightly on the baking sheet before transferring to a wire rack to cool completely. Serve and enjoy!