Preheat the oven to 325°F. Line the bottom and sides of an 11x7-inch (or 8x8) baking pan with parchment paper, leaving an overhang on two opposite sides. Lightly grease with cooking spray and set aside.

Cut butter into chunks. Combine the butter, sugar, cocoa, and salt in a medium microwave-safe bowl. Microwave for one minute intervals, stirring in between until the butter is melted and the mixture is smooth. Set the mixture aside until it cools slightly, it should be warm but not hot.

Stir in the vanilla with a wooden spoon or rubber spatula. Add the eggs one at a time stirring vigorously after each addition. When the batter looks thick, shiny, and well blended, fold in the flour just until incorporated and no streaks remain. Spread the batter into the prepared pan and bake 20-25 minutes, until just set. Let cool slightly then refrigerate until cool to the touch.

To prepare the chocolate glaze, in a small microwave-safe bowl, combine the chopped dark chocolate and butter. Microwave for 30 seconds and stir and continue to microwave 15 seconds at a time, stirring in between until smooth. Remove brownies from the fridge and evenly spread the glaze on top. (I used the back of a spoon.) Either cool the chocolate glaze by putting the brownies back in the fridge or leave it on the countertop. Once chocolate is set, cut the brownies into small squares.