Line a 9 x 9-inch pan with non-stick foil or plain foil sprayed with non-stick cooking spray; set pan aside. Preheat oven to 350ºF (175ºC).
From the 6 ounces of chopped semi-sweet chocolate, set aside 2 ounces for the ganache. From the 11 tablespoons butter, set aside 2 tablespoons for the ganache. Use the remaining chocolate and butter for the brownie batter.
In a microwave-safe bowl, combine the reserved chocolate-and-butter portion for the batter. Microwave at 30-second intervals, stirring between intervals, until the chocolate and butter are melted and the mixture is smooth. Let the mixture cool 5–10 minutes.
In a large bowl, whisk together 1 1/4 cups sugar, 3 eggs, 1 1/2 teaspoons vanilla, and a dash of salt until combined and slightly thickened.
Whisk the cooled chocolate-and-butter mixture into the egg mixture until uniform.
Stir in 1 cup flour just until incorporated and no large streaks of flour remain. Do not overmix.
Pour the batter into the prepared 9 x 9-inch pan and spread evenly. Bake 26–28 minutes, or until a tester inserted into the center comes out with moist crumbs (not wet batter). Remove from oven and place the pan on a wire rack to cool completely.
When the brownies are completely cool, make the chocolate ganache: place the reserved 2 ounces chopped chocolate and the reserved 2 tablespoons butter in a small microwave-safe bowl. Microwave at 15–20 second intervals, stirring between intervals, until the chocolate and butter are melted and the mixture is smooth. If needed, stir until glossy and pourable.
Pour the ganache over the cooled brownies and use an offset spatula or the back of a spoon to spread it to the edges in an even layer. Let the topping set at room temperature until firm, about 30–60 minutes.
To serve, lift the brownies from the pan using the foil, peel back the foil, and cut into squares.