Place the peeled sweet potatoes in a large pot. Add water to cover, then heat the pot over high heat and bring to a boil. Reduce heat to medium and continue cooking for approximately 30-50 minutes, until sweet potatoes are tender (less time for smaller sweet potatoes, more time for larger sweet potatoes).
Remove the sweet potatoes from the pot with a slotted spoon, and place in a large mixing bowl. Let sit for a few minutes.
Meanwhile, preheat oven to 350 degrees F. Grease a medium casserole dish.
Add 1 tablespoon of melted butter to the bowl with the sweet potatoes. Mash the sweet potatoes with the butter, then mix in the salt and pepper. Pour the mashed sweet potatoes into the greased casserole dish.
In another mixing bowl, combine the crumbled bacon, dried cranberries, breadcrumbs, maple syrup, chopped walnuts, and the remaining 1 tablespoon of melted butter. Spoon mixture over the mashed sweet potatoes.
Bake uncovered for about 25 minutes, until the topping is golden brown and mashed sweet potatoes are hot.