Prepare an 8x8 square pan with parchment paper.
Prepare and bake brownies according to package directions in the prepared pan, then allow to cool.
Prepare the frosting while the brownies are cooling. Add butter to a stand mixer or large bowl with an electric mixer and beat until light and fluffy. Add confectioner’s sugar in batches and beat until well combined. Add heavy whipping cream, then fold in peppermint candies and food coloring.
Top the cooled brownie base with buttercream frosting, spread evenly, then refrigerate or freeze while preparing the ganache.
Add cream to a microwave-safe bowl and heat on high for 60 seconds or until beginning to steam. Immediately add chocolate chips and cover for 3 minutes, then whisk until creamy.
Pour ganache over frosted brownies, and sprinkle the crushed peppermint candy over top of the ganache. Chill in the freezer until the ganache is set – about 20 minutes.
Remove brownies from the pan to a cutting board using the parchment paper, then cut into squares and serve.