Preheat oven to 350°F. Line an 8″x8″ baking dish with parchment paper and set aside.
In a microwave-safe mixing bowl, melt the butter. Stir in oil, sugar, eggs, vanilla extract, peppermint extract, salt, and optional coffee. Once combined, fold in cocoa powder and flour.
Pour the brownie batter into the baking dish, spreading evenly to the edges. Bake for 35 minutes, then remove from oven and allow to cool completely in the pan (about 1 hour).*
Make the peppermint frosting
While the brownies are cooling, make your frosting! In a standing mixer with a wire whip, cream the unsalted butter for 1 minute, then add the rest of the frosting ingredients and whip for an additional minute.
Once the brownies are cooled, spread the frosting evenly over the brownies, creating a smooth surface at the top. Place back into fridge for 15 minutes.
Make the peppermint bark
Once the frosted brownies have chilled, melt your chocolate and butter in a microwave-safe bowl in increments of 30 seconds, stirring in between each time.
Pour the melted chocolate mixture over the frosting, spreading to the edges and smoothing evenly with the back of a spoon. Top with crushed peppermint candies and allow to harden in fridge for about 1 hour. Then cut and serve!