Preheat the oven to 325 degrees F. Butter an 8 by 8-inch square pan and set aside.
In a small saucepan, melt the butter and bring it to just below a boil. Place the chopped chocolate in a large bowl. Pour in the hot butter and let stand for 30 seconds. Stir until completely melted. Sift in the sugar and cocoa powder. Beat in the mascarpone, eggs, and vanilla, mixing until smooth. Gently fold the flour and salt into the batter.
Pour the batter into the prepared baking pan and spread evenly. Bake for 45 to 50 minutes, or until a wooden skewer inserted into the center comes out clean. Cool for 10 to 15 minutes.
Spread the warm Ganache over the brownies. Allow the Ganache to set completely before cutting into squares.
Place the chocolate in a large mixing bowl and set aside. Bring the cream and butter to just below boiling point in a small saucepan over medium heat. Pour the hot mixture over the chocolate and let stand for 30 seconds. Stir the mixture until smooth.
The ganache should be used for spreading while warm.