Pour the batter into the prepared dish. Bake for 25-30 minutes or until a toothpick inserted in the center comes out mostly clean. We want it to be slightly gooey for a more moist texture!
For the frosting: start by melting the butter in a saucepan over medium heat, stirring occasionally. Once melted, the butter will begin to foam. Keep stirring occasionally. After 5-8 minutes, the butter will begin browning.
You’ll notice lightly browned specks begin to form at the bottom of the pan and it will have a nutty aroma. Once browned, remove from heat and pour into a heat-proof bowl. Refrigerate until solid.
Once blondies have cooled, evenly cover the top with frosting. Cover and store in the fridge until ready to serve. They’ll taste best if you let them sit overnight!