Preheat oven to 400°F. Prick sweet potatoes and Russets with a fork and spray with cooking spray. Season skins with salt and pepper and roast to almost tender but not fully cooked, 45 minutes. Cool.
Raise oven temp to 450°F. Halve potatoes and scoop out the potatoe leaving a half-inch layer on the skins. (Reserve the insides of potatoes to make hash brown cakes the next day.) Spray cut side of skins with cooking spray, season with salt and pepper, and roast to crisp.