Preheat oven to 350 degrees and spray a 12-cup Bundt pan with baking spray with flour.
Sift the all-purpose flour, cake flour, baking powder, baking soda, and salt together onto a piece of wax paper.
In a medium bowl, combine the chopped Heath bars and chocolate chips. Add 1 1/2 tablespoons of the flour mixture and stir together.
Using an electric stand mixer with a paddle attachment, cream the butter at medium speed for 3 minutes.
Add half the granulated sugar and beat for 2 minutes.
Add the remaining granulated sugar and beat for 1 minute. Scrape down the sides of the bowl.
Add the brown sugar and beat for 2 minutes.
Beat in the eggs, one at a time, beating for 45 seconds after each addition. Scrape down the sides of the bowl.
Add the vanilla extract.
With mixer on LOW speed, add the flour mixture in 3 additions, alternating with the sour cream in two additions. Stop a few times to scrape down the sides of the bowl.
Stir in the Heath bar/chocolate chip mixture. Transfer batter to the Bundt pan. Place it on a baking sheet in case any overflows. (It shouldn't unless you are using a smaller bundt pan but it's best to be safe.)
Bake for 55 to 60 minutes or until a toothpick inserted in the center comes out clean.
Let cool in the pan for 10 minutes and then invert onto a serving platter.
Once cool, sift powdered sugar over the cake.
You can use unsalted butter instead of salted. Change the salt amount to 3/4 teaspoon.