Fill a medium sized pot half way with water. Bring water to a boil on medium heat.
Once boiling, place sweet potatoes inside pot and continue boiling until potatoes are soft, about 45 minutes.
Preheat the oven to 400 degrees and spray casserole dish with non-stick spray.
Drain potatoes and set aside to come to room temperature. Once cooled, remove the skins and place the de-skinned potatoes inside a large mixing bowl. Mash the potatoes with an electric mixer.
Add the 1 cup of unsalted butter, orange juice concentrate, brown sugar, and orange zest. Blend until well mixed.
Place contents into casserole dish.
Place the topping ingredients in a small saucepan and bring to a boil under medium heat.
Pour melted topping over the sweet potato casserole and bake for 30 minutes or until topping is firm.