Peel sweet potatoes and cut into 1-inch cubes. Place in a large saucepan and cover with salted water. Bring to a boil. Reduce heat, cover, and simmer 10 to 12 minutes or until fork-tender. Drain. Add the zest and juice from 1 orange, 2 tablespoons butter, and a dash of salt. Beat with an electric mixer until the potatoes are light and fluffy.