Preheat oven to 350 degrees. Grease and line a 9x12 baking dish with parchment paper to make it easy to lift the brownies out of the pan.
Using a medium saucepan, melt the butter and chocolate chips together over medium low heat. Remove from the heat just before all the chips have fully melted, stirring to complete the process. Move the melted mixture into a glass bowl to cool a bit. Stir in the sugar, vanilla and coffee granules.
In another bowl, whisk the four eggs until bubbly on top - about one minute. Combine with the chocolate mixture, and then add the dry ingredients (flour, cocoa powder and baking powder). Stir until just combined, then pour into the baking dish, and bake for 30 minutes, until just barely cooked through.
As soon as the brownies come out, top with the mint candies, allowing the heat of the brownies to melt them. Using a small spatula, spread the melted mints into a thin smooth layer on top of the brownies, then chill for about one hour to set. The topping will be like an invisible layer of chocolate mint crust that is amazing!