Preheat your oven to 350°F (176°C) and lightly grease a 9" x 13" casserole dish.
Peel the sweet potatoes and cut into 2 inch pieces. Meanwhile, bring a pot of water to a boil. Add the sweet potatoes to the water and boil until they are fork tender, about 15-20 minutes. Drain the water and place the sweet potatoes into a large bowl.
To the bowl add, 6 tablespoons of melted butter, 2 tablespoons brown sugar, salt and cinnamon. Use a wooden spoon to mash the potatoes and blend the ingredients together. Leave the mixture as chunky or smooth as desired. (If you want a super smooth consistency, blend with an immersion blender.) Transfer the mixture to a lightly greased casserole dish.
To a small bowl, add the chopped pecans, 2 tablespoons melted butter, 2 tablespoons brown sugar and toss to coat evenly. Sprinkle the pecan mixture evenly over the top of the sweet potatoes.
Bake the casserole until it is heated through, about 45-60 minutes. (If the casserole is straight out of the fridge, it will require a longer bake time to be heated through.)