01 -  Preheat oven to 350°F. Line a 9x13-inch baking pan with parchment paper, allowing an overhang for easy removal. 
 02 -  In a medium mixing bowl, whisk together the all-purpose flour, baking soda, and salt. Set aside. 
 03 -  In a large bowl, whisk melted unsalted butter with light brown sugar and granulated sugar until smooth. Add eggs and vanilla extract, blending until fully incorporated. 
 04 -  Gradually fold the dry ingredients into the wet mixture, stirring just until combined. 
 05 -  In a small bowl, blend softened unsalted butter, light brown sugar, and ground cinnamon together to form the cinnamon swirl mixture. 
 06 -  Spread approximately two-thirds of the cookie dough evenly in the prepared pan. Dollop the cinnamon swirl mixture over the dough and gently swirl it using a knife or offset spatula. Drop spoonfuls of the remaining dough over the top, gently spreading to cover as much surface as possible. 
 07 -  Transfer pan to the oven and bake for 23 to 26 minutes, or until the edges are golden and the center is just set. Avoid overbaking. 
 08 -  Allow bars to cool completely in the pan on a wire rack before glazing. 
 09 -  Whisk powdered sugar, milk, and vanilla extract in a bowl until smooth. Drizzle the glaze over cooled bars, then slice into squares.