Preheat oven to 350°F.
Beat brown sugar, butter, eggs, corn syrup and vanilla in large mixer bowl until well blended. Slowly add in flour, cocoa powder, salt and baking powder. Beat until combined. Stir in chocolate chips and all but 1 cup of the mint candies.
Press into a greased 13×9 inch pan. Bake for 18 to 22 minutes until cookie bars are set but still soft. Sprinkle the reserved candies on top. Cool and cut into squares.