4ounces(113g)bittersweet or semisweet chocolate, chopped
Preheat the oven to 325 degrees F. Lightly grease a 9X13-inch aluminum pan with nonstick cooking spray and cut parchment paper to fit the bottom of the pan. Lightly grease the parchment paper. Set the pan aside.
For the brownies, in a small saucepan, melt the butter and chocolate, stirring until smooth. Set aside to cool slightly.
In a large bowl, combine the sugar, eggs and salt. Mix with a handheld mixer or in the bowl of a stand mixer for 3-4 minutes, until the mixture has lightened in color and is very thick.
Fold in the warm (not hot!) chocolate/butter mixture. Stir in the flour and vanilla extract. Mix until well combined. Pour the batter into the prepared pan, smoothing evenly.
Bake the brownies for 25-30 minutes until the sides pull away from the pan just slightly. Remove the brownies from the oven and cool completely on a wire rack (about 1 1/2 hours).
For the browned butter frosting, place the stick of butter in a small saucepan and set it over low heat. It is best to not use a non-stick or dark coated pan in this step because it will be difficult to tell when the butter has turned brown. Let the butter melt over low heat and turn a caramel brown color, about 15 minutes. Watch carefully so the butter doesn’t burn. Once it has turned a nice medium-brown color, remove it from the heat.
Pour the butter into a medium bowl. Immediately add the powdered sugar, heavy cream and vanilla. Mix well with an electric mixer until the frosting is smooth and thick.
Spread the frosting over the cooled brownies.
For the glaze, melt the butter and chocolate together in the microwave or on the stovetop until it is smooth. Pour the warm glaze over the frosted brownies. Tip the pan from side to side to even out the glaze over the frosting (or carefully spread with a knife or offset spatula).
Chill the brownies until the glaze is set and the brownies are chilled through, about 1-2 hours. The brownies taste best cold.