Peel the sweet potatoes (optional) and roughly chop them into large, even pieces. Place in a saucepan and cover with water. Bring to a boil and simmer the potatoes until they are fork tender.
Drain the potatoes and return to saucepan.
Add in the milk, maple syrup, butter, nutmeg, cinnamon, and eggs. Use a potato masher to moosh the potatoes until broken down. Just moosh until you're happy with the texture. I don't mind chunky potatoes, so I didn't moosh too much. Just enough to mix everything in.
Taste. Season with a pinch of salt, if necessary.
Divide the potatoes evenly among oven-safe ramekins. Top each ramekin with some walnuts.
Bake in a preheated 350 degree oven until bubbly and warmed thoroughly, about 20 minutes.