Combine the butter and sugars in the bowl of a stand mixer and beat on medium-high for 2-3 minutes.
Scrape down the sides, add in the egg and vanilla and continue beating for 7-8 minutes.
Reduce the mixer to low speed and add in the flour, baking powder, baking soda and salt until just combined (don't overwork the mixture or it can become tough).
Add in the chocolate, marshmallows, potato chips and pretzels (I break up the latter 2 into smaller pieces) and once again beat until just combined.
Using an ice cream scoop, portion out the cookie batter onto lined baking trays - I fit 6 cookies per tray.
Transfer trays to the fridge and allow to chill for at least an hour or overnight - do not bake these from room temperature as they won't hold their shape.
Preheat your oven to 190°C.
Put in your first 2 trays and bake for 18 minutes or until golden brown around the outside.
Cool the cookies completely on your trays before transferring to an airtight container for storage.