Preheat your oven to 400F. Prick the sweet potatoes a few times with a fork. Place them onto a lined baking sheet. Bake for 45-60 minutes, or until they're completely tender when pierced with a fork or knife. Reduce the oven heat to 350F.
Wearing oven mitts, cut the hot sweet potatoes in half and scoop out the flesh into a medium sized mixing bowl. Add the butter, non-dairy milk, maple syrup, and cinnamon. Mash roughly with a fork. The sweet potatoes should be mashed, but they should still have a bit of texture—you're not aiming for totally smooth or uniform.
Lightly oil or butter 2 or 3 small baking dishes. Transfer the mashed sweet potatoes to the dishes. Refrigerate for 1 hour.
To make the topping, place the butter, flour, sugar, cinnamon, and salt, if needed, in a small bowl. Use your fingers to crumble it all up. You're aiming for pea-sized pieces of butter and for everything to be well incorporated. Add the nuts and mix again.
Distribute the topping over the mashed potatoes in their little dishes. Transfer to the oven and bake for 25-30 minutes, or until the topping is golden brown. Serve.