Wash the sweet potatoes and dry them with a paper towel. Put the sweet potatoes on one of the baking sheets and pierce them with a fork.
Wash the broccoli and cut it into florets. Put the broccoli on the 2nd baking sheet in a single layer.
Put the sweet potatoes and broccoli in the oven and set the timer for 25 minutes.
When the time beeps, take out the broccoli. Set the timer for 35 more minutes.
Sprinkle the broccoli with salt and pepper to taste.
After the timer beeps again, take out the sweet potatoes. Let them cool for 10 minutes.
Cut the sweet potatoes with half and carefully scoop out the flesh with the fork (preserve the skin shell). Put the sweet potato pieces in a bowl and sprinkle with cinnamon. Mash sweet potatoes with a potato masher. If desired, add some butter and maple syrup to taste. Carefully mix in broccoli, dried cranberries and walnuts.
Put the mashed sweet potato mixture back into the sweet potato skin shells.