Scalloped potatoes are definitely decadent. Because the heavy cream and cheese aren't enough, I always include caramelized onions too, making them even richer. The onions need to be started on their own in the slow cooker, just to get the caramelization process started, but only for about half an hour. They'll continue to cook along with the potatoes for another 5 hours so doing it this way actually takes less time and effort than standing over the stove.
I do find the cream needs to be thinned out a bit first with chicken or vegetable broth; otherwise it just gets too thick and gluey over the long cooking process. Subbing chicken broth for some of the cream also makes this version of scalloped potatoes seem a bit lighter, but also tasting even more indulgent at the same time.
Pro tip: For a fun twist, switch out half of the Yukon Gold or russet potatoes for sweet potatoes - they pair perfectly with Parmesan!