In a medium bowl combine all ingredients except apples
Using a pastry cutter (or with your hands) work the butter into the dry ingredients until mixture is crumbly - set aside
Wash apples & cut off the tops
Spoon out some of the core & inner flesh to make a "bowl"
Fill each hallow apple with your crumble mixture & place inside your crock pot
Cover & cook 2-2.5 hours - just enough that the apples soften but are not falling apart
Serve with a scoop of ice cream or whipped cream on top (I like to add some caramel too)