Preheat your oven to 350°F. Grease and line a 9x9 inch baking dish with parchment paper. Set aside.
In a large bowl, combine your melted butter and brown sugar. Whisk together until incorporated. Add in your egg and vanilla extract. Whisk until combined.
Add your flour, baking soda, and salt to the wet ingredients. Fold the dry ingredients into the wet ingredients until just combined and you no longer see dry streaks of flour.
Pour the blondie batter into your prepared baking dish. Bake in the center of your preheated 350°F oven for 20 to 25 minutes, or until golden brown on the outside and a skewer inserted into the center comes out with just a few moist crumbs. Cool slightly before slicing and serving.
* Both light and dark brown sugar work perfectly for blondies. Use light brown sugar if you like a milder caramel flavor and dark brown sugar for more caramel punch!