Preheat the oven to 350 ̊F. Coat a 10-inch cast-iron skillet (measured across the top) with cooking spray.
Stir together flour, baking powder and salt; set aside.
Combine the chocolate and butter in a large, heatproof bowl. Set over a pan of gently simmering water and heat, stirring constantly, until melted. Remove from heat and whisk in sugar. Whisk in the eggs, one at a time, followed by the vanilla. Whisk vigorously for 30 seconds. Gently stir in flour mixture in two additions using a rubber spatula, then fold in half the chopped candy bar pieces.
Spread batter evenly into prepared skillet; smooth top. Scatter the remaining candy bar pieces across the top of the batter.
Bake for 24 minutes or until only a few moist crumbs adhere to a toothpick when inserted into the center of the brownie. Let cool slightly.
To make the chocolate sauce, combine the AMERICAN HERITAGE Chocolate Finely Grated Baking Chocolate and cream in a small, heatproof bowl. Set over a pan of gently simmering water and heat, stirring constantly, until a smooth ganache forms. Drizzle over the warm brownie just before serving. Top with vanilla ice cream if you like!