Peel sweet potatoes and cut into large chunks.
Place in a large pot stainless steel. Cover with water and bring to a boil. Reduce heat and cook potatoes until tender, about 20 minutes.
Drain potatoes and return to the pot.
Preheat oven to 350 degrees F. Spray a 9 x 13 pan with nonstick spray.
Add the melted butter, milk, maple syrup, vanilla, salt, and eggs to the pot. Using a hand mixer, mix until creamy and smooth.
Spoon the sweet potato mixture into the prepared baking dish in an even layer. Set aside.
In a small bowl, use a small wooden spoon to mix together the melted butter, brown sugar, flour, oats, and cinnamon. Crumble streusel over the sweet potatoes.
Bake at 350 degrees for 30-45 minutes, until lightly golden brown on top.
Let cool slightly and serve.