Preheat oven to 325°F and spray a large baking sheet or 13x18 baking sheet with edges with nonstick cooking spray (or line with parchment paper).
Over medium heat in a medium sized saucepan, melt butter and unsweetened chocolate. You want the mixture to melt completely and become smooth. ( You can also use a microwave- just heat for 30seconds, stir, repeat until melted and smooth)
While butter mixture is cooling, in a small bowl combine the flour, baking powder, and salt. Set aside.
In a stand mixer with the whisk attachments, whisk together the butter mixture (it’s okay if it’s still warand the sugar. Add the eggs one at a time, letting each egg become fully incorporated into the batter before adding the next Once the eggs are all added, mix in the vanilla.
By hand, with a large rubber spatula or mixing spoon, fold in the flour Folding in the flour will help the brownie batter keep the air in it.
Fold in candy pieces.
Pour into baking sheet and bake for 15-17 minutes or until a tooth pick comes out clean. If using a 9x13 you will cook them for 25-30 minutes.
Let cool for at least 30 minutes.*