Preheat oven at 350 degrees F. Line and grease a 8×8 baking pan. Set aside.
In a mixer, cream together butter and sugar until smooth. Add the melted chocolate and mix. Add eggs, 1 at a time then vanilla, bourbon and salt. Mix until all is well combined then add the flour.
Transfer mixture into the baking pan. Bake for 20-25 minutes, or until a knife inserted comes out clean.
While the brownies are baking, make the brown butter frosting. Add 1 stick of butter into a saucepan. Over medium heat, melt for about 3-5 minutes, until the butter foams and little brown specks appear. Be careful not let it burn!
Once the butter turns an amber color and has nutty aroma, remove from the heat and pour into a small bowl. Place the brown butter in the freezer for about 5-10 minutes to cool down. We need room temperate brown butter to continue.
In a bowl, add brown butter, powdered sugar, vanilla, sea salt, and heavy cream. Mix it all together for about 3 minutes for ultimate fluffiness.
Once the brownies have cooled, pour the frosting over the top and spread it evenly. Add sprinkles too, if desired. Serve and enjoy!
Brown Butter Frosting adapted from A Cozy Kitchen.