Peel and dice sweet potatoes. Cook in a pot with water until soft.
Preheat oven to 350 degrees F.
Once potatoes are cooked, drain and mash. Add butter, brown sugar, vanilla, salt and eggs. Mix well. Using a whisk helps. Spread potato mixture in prepared casserole dish. Set aside.
In another mixing bowl, mix together sugar, flour, salt and nuts. Add melted butter and stir with a fork, until it forms crumbly dough.
Sprinkle the topping over the mashed potatoes.
Bake casserole for 25 minutes. If desired, add mini marshmallows. Place dish back in the oven and bake until the marshmallows are toasted, about 3 to 5 minutes.
Cool before serving.
Notes
To reheat a sweet potato casserole, preheat oven to 300 degrees F. Cover the dish with aluminum foil, to prevent the brown sugar pecan topping from burning, and bake for about 15 minutes.