Scrub and bake sweet potatoes. You will need 3 cups so 3-4 potatoes. Bake at 375 for 1 to 1 1/2 hours until very soft.
Allow to cool and then peel. You may refrigerate at this point until needed.
In a large mixing bowl beat 3 cups sweet potatoes until smooth.
In a separate bowl beat together two eggs, 1/4 cup sugar, 1/2 teaspoon salt, 1/2 stick melted butter, 1 1/2 teaspoon vanilla, 1/2 cup milk. Beat well.
Add to sweet potatoes and mix well.
Place into a well oiled (Pam or butter) oven safe bowl.
Chop pecans. Mix topping in a medium bowl. 1 1/2 cup of brown sugar, 1/2 cup flour, 1/3 stick melted butter and 1/2 cup chopped pecans.
Add topping to sweet potatoes. You may cover and refrigerate at this point for 3 days maximum per the FDA. Bake at 350 for 30-35 minutes.
Bake at 350 for 30-35 minutes until golden brown and 165 minimum internal temperature.
Precook the sweet potatoes the day ahead.
You may substitute mini marshmallows for the topping if you want. 1 1/2 to 2 cups should do it. Cook to nicely brown with at least 165 internal temperature which should be about the same amount of time.
The FDA says three days refrigerated is fine. I would prefer to cook and mash the potatoes and mix the topping ahead. Then assemble just before cooking.