Preheat the oven to 350 degrees F and line a baking sheet with parchment paper. Cream the butter and sugars together until light and fluffy. Add the egg and mix well. Beat in the vanilla.
In a separate bowl, whisk together the flour, baking soda and salt. Add the flour mixture to the butter mixture and mix until just incorporated. Add in the rolled oats, pistachios, chocolate and cranberries. Stir until combined.
Form the dough into 2-tablespoon balls. At this point, you can either freeze the cookies or bake them. If freezing, make sure to freeze the cookie balls on a lined sheet with space in between the balls. When frozen solid, pop them into a freezer bag.
If baking right away, place the cookie balls on the prepared baking sheet and lightly flatten. Make sure the cookies are well spaced as they will spread. Bake until golden brown and just set, 14 to 16 minutes. Remove from the oven and cool for 5 minutes on the sheet, and then move to a wire rack to cool completely.
To bake from frozen, pull the cookies out of the freezer and place on a lined baking sheet to thaw slightly while preheating the oven. Add a couple of extra minutes on the bake time.