Peel sweet potatoes, cut into small chunks, and add to a small pot with water to cover. Add 1 tsp. salt to water. Bring to a boil and boil for 20 minutes.
Meanwhile that's boiling, in a small saucepan add rest of ingredients except marshmallows. Bring to a boil, stirring a little. Remove from heat and add vanilla.
When potatoes are done, drain water and put potatoes into a 2 1/2 qt. casserole dish. (I use my oval white corningware one.)Sprinkle with pecans, then pour sauce over all. Toss GENTLY to coat. Arrange so that all the pieces are submerged as much as possible. Bake, uncovered, in 350 degree oven for 40 minutes. (I give the potatoes a gentle stir to turn them halfway through. Be careful doing this, sauce will be very hot and potatoes can fall apart easily. (Turn carefully.) Remove from oven and turn oven to low or medium broil. Top evenly with a nice layer of marshmallows completely covering. Place into oven and watch!! As soon as they start to poof up and brown remove them immediately or they will catch fire. If they burn...scrape top off into sink, retop with second half of bag of marshmallows and call do-overs! ;) :D Serve warm.