In KitchenAid (or with electric handheld mixer) on medium speed, cream together butter and shortening.
Add Peanut Butter and sugars and vanilla and beat on medium-high speed until creamy and well combined, about 1-2 minutes (scrape down sides of bowl with rubber spatula if necessary).
Add eggs and egg yolk, one at a time, beating well after each addition.
Stir in heavy cream.
In separate, medium-sized bowl combine flour, baking soda and salt.
With mixer on low-medium speed, gradually add flour mixture to peanut butter mixture, pausing occasionally to scrape down sides of bowl to ensure all ingredients are well combined.
Cover and refrigerate at least one hour.
Preheat oven to 375F.
Using ice cream scoop or 1/4-cup-sized measuring cup, scoop large balls of dough onto parchment paper-lined cookie sheet.
Press down on dough to flatten slightly with fingers or with bottom of a clean glass (cookies will spread more when baking, only flatten to about half their scooped height).
Bake on 375F for 13 minutes.
Allow to cool on cookie sheet for 5 minutes before transferring to wire rack to cool completely.
Once cookies are cooled completely, melt chocolate chips in microwave-safe bowl on 15 second increments, pausing every 15 seconds to stir.
Hold cookie over bowl of chocolate and, using a spoon, spoon chocolate over half of cookie (this is a much cleaner tactic than actually dipping the cookies in the milk chocolate).
Return to rack and immediately sprinkle with heath bar bits. Repeat with each cookie.
Allow chocolate to harden before eating.
It is important that the dough be well-chilled so that it does not spread too much when baking. If you are using the same cookie sheet for multiple sets of cookie dough, make sure the sheet has cooled completely before placing more cookie dough on it.