Preheat your oven to 350°F (175°C) and grease a 9×13-inch baking dish.

In a large mixing bowl, whisk together melted butter and brown sugar until combined. Add eggs and vanilla extract, stirring until smooth. Fold in flour and salt until just combined.

In another bowl, mix brown sugar, cinnamon, and melted butter until resembling wet sand. Set aside.

Spread blondie batter evenly in the baking dish. Drop spoonfuls of the cinnamon swirl mixture over it, then swirl gently with a butter knife.

Bake in preheated oven for 25-30 minutes until golden edges form. Cool completely in the pan.

In a bowl, beat cream cheese until smooth. Gradually add powdered sugar, milk, and vanilla, mixing until creamy.

Drizzle icing over cooled blondies, cut into squares, and serve.