Preheat your oven to 350°F (175°C). Grease a 9x9 inch baking pan or line it with parchment paper for easy removal.
In a large mixing bowl, whisk together the melted butter and brown sugar until smooth. Then, add in the egg and vanilla extract. Mix until fully incorporated.
In another bowl, combine the flour and salt. Gradually add this dry mixture to the wet ingredients, stirring gently until just combined. Do not overmix; a few lumps are okay!
Pour the batter into the prepared baking pan, spreading it evenly. Bake in the preheated oven for about 20-25 minutes or until a toothpick inserted in the center comes out with a few moist crumbs (not wet batter).
While the blondies are baking, prepare the caramel topping. In a saucepan over medium heat, melt the ¼ cup of unsalted butter. Stir in the brown sugar and half-and-half, whisking until the mixture comes to a gentle boil. Continue to cook for about 2-3 minutes, stirring constantly until thickened.
Remove the saucepan from heat and stir in the vanilla bean paste. Gradually whisk in the sifted confectioners sugar and optional salt until smooth. Set aside to cool slightly.
Once the blondies are finished baking, remove them from the oven and allow them to cool in the pan for about 10 minutes. Pour the caramel topping over the warm blondies, spreading it evenly with a spatula. Let it set for a few minutes before slicing into squares.