Preheat oven to 350˚F. Whisk together cocoa and baking soda. Stir in melted butter. Add the boiling coffee and stir until the mixture thickens
Stir in the sugar and eggs until smooth. Mix in the flour, vanilla, and salt.
Spread in a greased 9×13 pan and bake at 350˚F for 35-40 minutes, just until the brownies start to pull away from the edges of the pan.
Mint Buttercream Frosting
Beat the softened butter until light and fluffy.
Add the sugar, 2 tablespoon of milk, and mint extract. Stir until combined, then beat until smooth.
Stir in the green gel paste or food coloring until it is the shade of green you want.
Spread over the cooled brownies.
Place in the fridge for 30 minutes so that the buttercream can set before adding the chocolate layer.
Chocolate Mint Icing
Melt chocolate chips, butter, and light corn syrup in the microwave at 50% power for 2 minutes. Stir and continue heating at 50% power for 30-second intervals and stirring until smooth.
Mix in the peppermint extract.
Pour over the mint buttercream frosting and spread to cover.
Return to the fridge to harden.
Drizzle with melted green candy melts before serving, if desired.
Notes
Store bars in an airtight container in the fridge for 3-4 days.