Preheat oven to 400 degrees F. Spray a 9x13 inch pan with non-stick cooking spray, or grease with butter.
In a small bowl, combine brown sugar and cinnamon. If adding salt, that can be added here as well. Mix well then set aside.
Pour drained yams/sweet potatoes into prepared baking dish. Spread them out so that they are evenly distributed in the pan.
Place small pieces of butter on top of the sweet potatoes, covering as many areas of the sweet potatoes as possible.
Sprinkle brown sugar mixture evenly over sweet potatoes and butter. Then sprinkle chopped pecans over brown sugar mixture.
Place pan in the center of the oven and bake for approximately 10 minutes. Remove pan from the oven and carefully sprinkle marshmallows over the top of the sweet potatoes, then return pan to the oven.
Bake for an additional 10-15 minutes, or until the brown sugar and butter mixture is bubbling and the marshmallows have reached your desired level of golden brown. Remove from oven and allow to cool for a few minutes prior to serving.