Melt the butter and chopped chocolate in a double boiler over simmering water, stirring frequently, until the mixture is smooth and fluid. Remove chocolate from double boiler and allow it to cool slightly.
In a large bowl beat the eggs and sugar with a hand-held electic mixer on medium speed. Continue beating until the eggs and sugar are pale yellow and thick, about 5 minutes. (It will look a bit like vanilla pudding.)
Mix in vanilla and salt.
Using a silicone spatula, gently fold in the chocolate mixture.
In a small bowl, whisk together flour and baking powder. Then gently fold it into the chocolate and egg mixture.
Stir in the chopped peppermint bark.
Spoon the batter into an 11 x 13 baking dish. Cover and place in the freezer for about an hour or until the batter is firm.
Preheat the oven to 350 degrees.
Scoop 2-tablespoon-size balls of dough on baking sheets lined with parchment paper.
Bake cookies 10-12 minutes until the edges are dry and the tops are cracked.
Allow cookies to cool for 10 minutes on the cookie sheets. Then transfer the cookies to cooling racks until completely cooled.