Preheat oven to 350 degrees. Spray 8-inch square pan with baking spray and set aside.
In a small bowl, whisk together the flour, baking powder and salt.
Melt butter and chocolate in a bowl set over a pan of simmering water (or a use double-boiler), stirring frequently until melted. Remove bowl from heat and let cool for a few minutes.
In a separate bowl, whisk the eggs and sugar until well-blended. Stir in vanilla and chocolate mixture. Fold in flour mixture until combined.
Pour batter into prepared pan. Place Mounds bars on top of batter, pressing down slightly. (I did 3 rows of 4).
Bake until just set, about 30 minutes. Let cool completely on wire rack.
Recipe by Alida's Kitchen at https://www.alidaskitchen.com/2012/10/25/mounds-brownies/