Preheat oven to 325 degrees F (160 degrees C) and place the rack in the center of the oven. Have ready a 9 x 9 inch (23 x 23 cm) square baking pan that has been lined with aluminum foil across the bottom and up two opposite sides of the pan. Set aside.

Brownies: In a stainless steel (heatproof) bowl placed over a saucepan of simmering water, melt the butter and chocolate. Remove from heat and stir in the sugar and vanilla extract. Add the eggs, one at a time, beating well (with a wooden spoon) after each addition. Stir in the flour and salt and beat, with a wooden spoon, until the batter is smooth and glossy and comes away from the sides of the pan (about one minute). Pour the brownie batter evenly into the prepared pan.

Bake in the preheated oven for about 25 minutes or until the brownies start to pull away from the sides of the pan and the edges of the brownies are just beginning to brown. A toothpick inserted in the center of the brownies will come out almost clean. Remove from oven and place on a wire rack to completely cool.

For the Mint Layer: In the bowl of your electric mixer or with a hand mixer, beat all the ingredients until smooth. Add a few drops of green food coloring if you want the frosting green. If the frosting is too thick, add a little extra cream. (The frosting should be just thin enough to spread.) Spread the frosting evenly over the cooled brownie layer. Place in the refrigerator for about 5-10 minutes or until firm.

For the Chocolate Ganache: In a heatproof bowl over a saucepan of simmering water, melt the chocolate and and cream.  Allow to col about 15 minutes.  Stir.   Spread over the mint filling and refrigerate for about 30 minutes.

To Serve: Remove the brownies from the pan by lifting with the ends of the foil and transfer to a cutting board. With a sharp knife, cut into  squares. It is a good idea to wipe your knife between cuts with a damp cloth. These brownies can be stored in the refrigerator for several days or else frozen.