Adjust oven rack to middle position and preheat oven to 350°F. Line an 8- by 8-inch baking dish with parchment paper. Butter paper.
In a small saucepan, combine butter and chocolate and cook over medium heat, stirring often, until just melted. Stir until smooth. Take off heat and stir in sugar.
Whisk in eggs one at a time. Stir in flour and salt until combined.
Add 1/2 of chopped peppermint bark to batter and stir to incorporate.
Pour batter into prepared pan.
Sprinkle top with remaining peppermint bark.
Bake until brownies are dry on top and just cooked through but still gooey in the center, about 25 minutes.