~ UPDATE ~
After cooking for 6 hours in phase two, the apple mixture smelled AMAZING but was still rather thin, so I set it to cook on high for about 45 minutes with the lid off to cook off some of the liquid. That seemed to do the trick. Next, I was looking for a smoother consistency, so I used an immersion blender to even out the texture, then let it sit for another half hour or so on low to really come together and get thick. (In case you're wondering, bedtime got moved back quite a bit! Next time I think I'll do phase one overnight and begin phase two in the morning.)
The 15 apples I started out with cooked down to about 7 cups of apple butter. On my last trip to the grocery store I was happy to discover that Ball (the canning company) now makes plastic 8 oz. freezer jars (in a pack of 5) perfect for projects like this.
Tomorrow's Apple a Day Recipe: Apple Spice Bundt Cake!