Boil water in a large pot and add sweet potatoes.
Cook for about 10 minutes, until fork tender.
Drain the water from the potatoes.
Add 6 Tbsp butter, 3 Tbsp brown sugar, 2 tsp cinnamon, 1/2 tsp nutmeg, and orange juice to the potatoes.
Mash until well incorporated.
In a medium bowl, combine chopped pecans, 2 Tbsp melted butter, 2 Tbsp brown sugar, 1/2 tsp cinnamon, and 1/2 tsp nutmeg. Stir to coat the pecans.
Grease a large baking dish.
Fill with the sweet potato mixture and top with the pecan topping mixture.
At this point, you can cover the casserole dish with plastic wrap and refrigerate it to bake later OR bake it right away.
If you bake it right away, preheat the oven to 350 F and bake for 30 minutes or until the pecans turn a golden brown and start to caramelize.
If you reserve it for later, you will want to bake it for 45-50 minutes, because you will be starting with a cold casserole.