Preheat the oven to 350°F. Grease a 9 x 13 cake pan.
In a large bowl, cream the butter and sugar with a mixer.
Add the eggs and the vanilla to the creamed mixture and mix until combined.
Sift the flour, cocoa, and salt and add them to the butter mixture. Stir just until combined. The batter will be very thick.
Spread the batter out in the bottom of the greased 9 x 13 cake pan.
Bake at 350°F for about 30 minutes, or until a toothpick inserted into the center comes out clean.
Let the brownies cool completely before continuing with the frosting.
Put all of the ingredients for the mint frosting in a medium sized bowl and beat until it is creamy and fully combined. Spread the frosting onto the cooled brownies.
Put the brownies into the fridge for the mint frosting to harden a bit while you work on the ganache.
For the ganache, begin melting the butter and chocolate chips together in a double boiler or a bowl on top of a sauce pan with a couple inches of boiling water.
When the chocolate begins to melt, warm the cream until it is warm to the touch and then add it to the melting chocolate. Stir until the chocolate is completely melted.
Spread the ganache on top of the brownies, being careful to not mix it with the mint frosting underneath.
Chill until the chocolate is set before cutting and serving.