Preheat oven to 350 degrees.
To make the brownies, melt the butter in the microwave in a large glass bowl. Stir in cocoa until smooth; allow to cool.
Combine the flour, baking powder and salt in a separate bowl.
When butter mixture is cool, stir in the honey, eggs, vanilla and sugar.
Blend in dry ingredients until well combined. Add walnuts if desired.
Pour batter into a greased 9x13 pan and bake for about 25 minutes. Cool.
Make mint frosting by mixing together butter, salt, corn syrup and powdered sugar and smooth. Add mint extract and green food coloring.
Add milk gradually until consistency is a little thinner than cake frosting.
Spread mint frosting over cooled brownies. Refrigerate to set frosting.
Meanwhile, make ganache by heating the cream over medium heat until scalding; do not let it boil.
Remove from heat and stir in chocolate and corn syrup. Stir until mixture is smooth and shiny.
Cool ganache until it is close to room temperature, but still pourable.
Pour ganache over mint frosting layer and spread evenly.
Return brownies to refrigerate to set ganache. Cut into squares, wiping your knife clean after each cut.