Preheat oven to 350 degrees F. Prepare a 9x13 pan with parchment paper or grease.
Add flour, baking soda, and salt to a mixing bowl, then mix together.
Add dark chocolate pieces and butter to a small microwave-safe bowl, then heat on high for one minute, stirring every 15 seconds.
Add chocolate butter, eggs, sugar, and extracts to a mixing bowl and beat until well combined.
Gently add flour mixture in batches and mix on low until just combined.
Pour into prepared pan, then bake for 28 to 29 minutes or until toothpick comes out clean. Allow to cool slightly on the counter, then refrigerate until cool.
Make peppermint frosting: Add confectioner’s sugar and butter to a large mixing bowl and beat until light and fluffy. Add in ½ cup peppermint pieces and heavy cream. Spread over cooled brownies.
Make chocolate ganache: Add ganache ingredients to a saucepan and heat over low-medium heat and mix until creamy, about 6 to 7 minutes. Allow to cool for 5 minutes, then pour/spread gently over frosting.
Top with 1 cup peppermint pieces, refrigerate for 1 hour, then cut and serve.