Preheat the oven to 350°F (175°C) and prepare a 9x13-inch baking pan lined with parchment paper.

In a large bowl, cream together the softened unsalted butter, light brown sugar, and granulated sugar until light and fluffy (3-4 minutes).

Beat in the eggs one at a time, then stir in the vanilla extract.

In a separate bowl, whisk together the all-purpose flour, baking soda, and salt. Gradually add this to the wet mixture, folding gently until combined.

Press half of the dough evenly into the bottom of the prepared pan.

Spread the warmed salted caramel sauce over the pressed dough and sprinkle sea salt flakes on top.

Crumble the remaining dough over the caramel layer, covering it well.

Bake for 30-35 minutes, until the edges are golden brown and the center is set yet soft.

Allow the bars to cool in the pan on a wire rack for at least 1 hour.

In a bowl, whisk together powdered sugar, milk or cream, and ground cinnamon until smooth. Pour over cooled bars and let set for 10 minutes.