Bake your sweet potatoes.  Preheat oven to 400.  Prick sweet potatoes with a fork.  Bake until soft, about 1 hour.(tip--place on nonstick foil covered cookie sheet before baking to avoid a drippy mess in your oven!)  Let cool slightly on rack.

Cut your sweet potatoes in half and carefully scoop out flesh into a mixing bowl, leaving a thick border for stability.

Prep filling: Mix  flesh until smooth, then stir in sour cream, softened butter, 1/2 cup brown sugar, lemon juice, nutmeg, cinnamon and salt & pepper.

Carefully spoon sweet potato mixture into 12 of the shells, dividing the mixture evenly
among them. (Note: you can also use a large pastry bag fitted with a large
round tip to fill shells).  At this point you can cover and refrigerate the potatoes overnight if necessary.

Heat oven to 350 degrees.  Sprinkle potatoes with a little brown sugar, then
top with one slice of butter each.  Arrange marshmallows on top.

Bake on a foil-covered rimmed baking sheet until hot and marshmallows are golden
brown, about 20-25 minutes.