Adjust oven rack to middle position and heat oven to 350 degrees F. Lightly spray a 9x13-inch baking dish with nonstick cooking spray.
Add chocolate and butter to a medium heat-proof bowl. Heat at 50% power in microwave for 1 minute. Stir, and heat at 50% power for 30 seconds. Stir and repeat until chocolate and butter are melted. Cool for 5 minutes.
In a large bowl whisk sugar, baking powder, salt, eggs, and vanilla together until combined. Pour in flour and whisk until just combined and no flour streaks remain.
Whisk in chocolate mixture until smooth.
Pour batter into prepared pan and spread evenly. Bake 45-55 minutes, or until toothpick inserted comes out clean.
FOR THE TOPPING:
Place the white chocolate chips and shortening in a medium microwave-safe bowl, and microwave on high for 30 seconds. Stir and continue to microwave for 30 seconds more and stir until smooth. Continue the process at 10-second intervals as needed (BE CAREFUL, because white chocolate can burn easily.)
Pour melted white chocolate onto cooled brownies and spread into an even layer.
Sprinkle with the chopped candy cane pieces. Cool on a wire rack until the brownies are cool and the white chocolate topping has firmed about 2-3 hours. Slice and serve!
To speed up the cooling and chocolate setting process, you can pop the brownies into the refrigerator for about 30 minutes.