Preheat the oven to 350 degrees. Grease a 9 inch round pan and line the bottom with parchment paper. Set aside.
Place the butter and chocolate into a large bowl. Melt in microwave - heat for 30 second intervals and stir between each interval until butter and chocolate are melted and thoroughly combined.
Add the sugar and stir to combine.
Let the chocolate mixture cool for 5 minutes. then whisk in the eggs one at a time, whisking until smooth after each addition.
Whisk in vanilla. Gently fold in flour and salt.
Pour the batter into the pan and bake for 25-30 minutes, or until a toothpick comes out clean. Let cool for 5 minutes and then run a thin knife along the side of the pan to loosen the brownie.
Let the brownie cool for another 10-15 minutes at room temperature and then chill the brownie, still in its pan for another 30 minutes. Remove from fridge and invert the pan onto your serving plate.
To make the frosting, place the butter and cream cheese in a bowl; beat with a mixer for 3 minutes or until thoroughly combined. Add the sugar, vanilla, salt and milk and beat for an additional 3-5 minutes on high until frosting is light and fluffy.
Spread the frosting evenly over the brownie base and top with fresh fruit and mint sprigs if desired.
Cut into wedges and serve, or cover loosely chill for up to 2 hours before serving.