Prepare oranges by cutting tops off, 1/4 to 1/2 inch down. Spoon out the flesh, leaving a shell.
In a large bowl combine sweet potatoes, sugar, orange juice, eggs, vanilla extract, 1/2 cup butter and grated orange peel. Spoon mixture into orange shells. Place in a deep casserole dish.
In a small saucepan over medium heat, combine remaining 1/2 cup butter, brown sugar, flour and pecans. Cook until sugar dissolves in melted butter. Spoon over oranges. Fill casserole dish with water to reach 1/2 inch in depth.