Peel the sweet potato and cut it up to fit in your steaming basket. Fill a suitable pot (one that will hold your steaming basket securely) with around 2-3 inches of water and bring it up to a simmer over medium heat. Place the basket over the pot and cook for around 15 minutes. Carefully, remove the sweet potato from the heat and allow it to completely cool.
Line a small bread tin or lunch box with greaseproof paper.
Add the dairy-free milk, cooled sweet potato, almond butter, maple syrup and vanilla extract to a blender and blend until smooth.
Either in the microwave or over a double-boiler melt the vegan chocolate.
With the blender running, stream in the melted chocolate and blend until well combined and smooth.
Pour the mixture in to the prepared bread tin, level and sprinkle with hemp seeds or any topping of your choice. Cover with foil and pop it in the freezer to set for at least an hour. When set, remove from the freezer and cut in to slices to serve.
Store in the freezer or for a softer mousse slice, the fridge.