Bring a large pot of water to a boil.
Remove the core from the cabbage but keep the leaves intact.
Carefully lower the cabbage into the water. Boil for 2 minutes then remove and let cool slightly before gently removing any softened leaves that will come off without tearing, Return the head to the water and continue boiling/removing leaves until you have 12 nice large leaves.
Chop any remaining cabbage and use it to line the bottom of your slow cooker.
Place the remaining cabbage roll ingredients into a large bowl and combine well.
Working in batches, lay out a cabbage leaf and spoon 1/3 cup of the meat mixture into the middle. Roll the leaf up like a burrito, folding the sides in to seal it as you go. Place into your slow cooker, seam-side down.
Place cooker on low. Add the sauce (see below), cover, and cook for 8 hours.
Let cool 15 minutes before serving with sauce spoon over the tops.