Preheat your oven to 350°F (175°C). Grease and flour an 8x8 inch baking pan.

In a medium bowl, combine the melted butter, light brown sugar, and granulated sugar. Mix well until everything is thoroughly combined.

Add the egg and vanilla extract to the butter and sugar mixture. Beat until the mixture is smooth and creamy.

Add the salt and flour to the wet ingredients. Gently mix until just combined.

Pour half of the batter into the prepared pan. Drizzle half of the caramel sauce over the batter. Pour the remaining batter over the caramel, then drizzle the remaining caramel sauce on top. Use a knife or skewer to swirl the caramel into the batter, creating a marbled effect.

Bake in the preheated oven for 25-30 minutes, or until a toothpick inserted into the center comes out with moist crumbs. The edges should be golden brown.

Let the blondies cool completely in the pan before cutting them into squares.