Preheat oven to 350°F. Butter 9x13” baking pan.
In medium bowl, whisk together flour, baking powder and salt. Set aside.
In bowl of electric mixer, beat butter, sugar and brown sugar until light and fluffy. Add eggs, one at a time, mixing well after each addition. Mix in vanilla.
Reduce mixer speed to low. Gradually add flour mixture, mixing just until combined. Stir in candies.
Transfer batter to prepared pan and spread evenly. Bake 30 to 35 minutes, or until bars are lightly browned and pick inserted into center comes out clean.
Place chocolate in heat-proof bowl.
Place cream in heavy saucepan and bring to boil over medium-high heat. Pour cream over chocolate and allow it to sit for about 5 minutes. Then stir the mixture until smooth to create ganache frosting.
Spread frosting over the bars or dip cut bars into ganache to coat top. Allow frosting to set before serving.