Turn your Slow Cooker on high to preheat. In a large mixing bowl combine the Graham Cracker Crumbs with the melted butter until all of the Graham Cracker Crumbs are moist.
Pour the moist cracker crumbs into the slow cooker and mold the cracker crumbs into the cooker (remember that it is hot) with a spatula.
Cover and cook on high for 45 Minutes.
Uncover and spread the chocolate chips and then the butterscotch chips over the cracker crumbs.
Pour the Sweetened Condensed Milk over the chips and graham cracker crumbs, covering the edges well along with the rest of the mixture.
Cover the mixture with marshmallows. Re-cover the lid and bake for an additional 1 1/2 to 2 hours and 15 minutes. You want the marshmallows melted, chocolate melted and the crumbs to harden with the sweetened condensed milk without burning. If you feel it is getting too brown on the edges you can turn on low or can turn off.
If you want a really gooey bar cookie, you can wait until it's just cool enough to be touched to serve. If you want a nice firm bar cookie you can wait until it's completely cooled off to cut and serve. I just stored it right in the casserole slow cooker with the lid, instead of removing and storing in a different container.