Place sweet potatoes in a large bowl. Beat with an electric mixer until light and fluffy. Mix in the butter, cinnamon, orange juice, eggs, salt, and liqueur. Transfer to a 2 quart casserole dish. Mix the pecans and brown sugar in a small bowl, and sprinkle evenly over the sweet potato mixture.
Bake 30 to 40 minutes in the preheated oven, or until center is firm and edges are lightly browned.
