Preheat your oven to 350°F (175°C).
Grease a 9x13-inch baking pan with butter or line it with parchment paper.
In a large mixing bowl, combine the melted butter, egg, light brown sugar, and vanilla extract. Whisk until fully blended.
Add the cinnamon, flour, and salt to the wet mixture. Stir until just combined; be careful not to overmix.
Pour the batter into the prepared baking pan and spread it evenly.
Bake in the preheated oven for 20-25 minutes, or until a toothpick inserted in the center comes out clean.
While the bars are baking, prepare the cream cheese frosting. In a medium bowl, beat the softened cream cheese and butter together until smooth. Gradually add the confectioners' sugar, vanilla extract, and salt, mixing until creamy.
Once the bars are baked, allow them to cool in the pan for about 10 minutes, then transfer to a wire rack to cool completely. Spread the cream cheese frosting evenly over the bars.
Sprinkle a little cinnamon on top for garnish.
