Scrub sweet potatoes and bake or boil until tender. Let cool, then peel and mash or purée.
Preheat oven to 350 F.
In a mixing bowl, beat together eggs, butter, pure maple syrup, vanilla extract, lemon juice, and salt.
Add sweet potatoes to egg mixture. When combined, transfer to a lightly greased 9 x 13 baking dish.
Make topping by combining brown sugar, chopped pecans, and butter. Set aside.
Bake until mixture is set and topping begins to bubble, about 30-40 minutes.
Remove from oven and top with pecan halves and marshmallows. Bake until marshmallows begin to brown, about 10 minutes.