Peel and slice and wash sweet potatoes. Place in large pot and boil until tender. Drain water from pot. Mash sweet potatoes until there are no lumps left.
To the mashed sweet potatoes, add in sugar, 3 Tbsp of butter, salt, vanilla, milk, and eggs. Mix until combined. Pour into greased pan.
Create the topping by combining light brown sugar, flour, 5 Tbsp cold butter, and chopped pecans. Sprinkle over top of casserole. Bake at 300° for approximately 30 minutes or until the topping is brown.