- Combine the butter and sugars in the bowl of a stand mixer fitted with the paddle attachment and cream together on medium-high for 2 to 3 minutes. Scrape down the sides of the bowl, add the egg, egg yolk and vanilla, and beat for 7 to 8 minutes.
- In a separate bowl, mix together the flour, baking powder, baking soda, cornstarch and salt. Reduce speed to low and add this mixture to the butter mixture. Mix just until the dough comes together, no longer than a minute. Scrape down the sides with a rubber scraper.
- Still on low speed, add the chocolate chips, heath bar bits, oats, and coffee and mix just until incorporated, about 30 seconds. Still on low speed, add the M&M's, potato chips and pretzels until just incorporated (just a couple of turns of the paddle). Be careful not to over mix or break too many of the potato chips.
- Using a 1.5 inch cookie scoop (about 2 tablespoons worth), portion out the dough onto a parchment-lined sheet pan. Pat the tops of the cookie dough domes flat and gently press additional M&M's and chocolate chips into the tops of the mounds. Wrap the sheet pan tightly in plastic wrap and refrigerate for at least 1 hour, but preferably 24-48 hours.
- Preheat the oven to 350 degrees.
- Place the cookie balls on a parchment-lined or silpat lined baking sheet, spaced about 2 inches apart. Bake for 10-12 minutes or until slightly browned on the edges. (They will appear undercooked in the middle when you take them out but they will firm up once they cool.) Allow to cool for 2-3 minutes on the baking sheet before transferring them to a wire rack to cool completely.
*If freezing the dough, flash-freeze the dough balls on the parchment-lined pans. Once frozen, transfer to an airtight container or freezer bag. They will need a few extra minutes in the oven once you bake them, but otherwise they should cook up just the same!
