In a large bowl or stand mixer, add 6 tablespoons softened butter and beat until creamy. Add 3/4 cup packed brown sugar and 1 1/2 tablespoons cinnamon. Beat until smooth.

Use a spoon to create small balls of filling, about the size of a marble. Freeze for 20 minutes on a lined baking sheet.

Preheat oven to 350 degrees F and prepare baking sheets with parchment paper.

In the same large bowl, beat 1 cup softened butter until smooth. Add 1 2/3 cup granulated sugar and beat for 2 minutes until light and fluffy.

Add 2 large eggs and 2 teaspoons vanilla extract. Beat until smooth.

Stir in 3 1/2 cups flour, 1 teaspoon baking soda, 3/4 teaspoon kosher salt, and 1 1/2 teaspoons cream of tartar.

Gently fold in the frozen balls of cinnamon filling using a wooden spoon.

Scoop dough balls (about 2 inches across) and roll them in a mixture of 1/3 cup granulated sugar and 1 1/2 tablespoons cinnamon.

Place cookie dough balls on prepared baking sheets with 2 inches between them.

Bake for 11-12 minutes until edges are firm but cookies will still look glossy.

Immediately reshape cookies with a couple spoons after baking.

Let cookies cool on the pan for at least 5 minutes before transferring to a wire rack.