Boil or bake yams until they are half cooked (before the yams get too soft). Peel and cut in 3/4" slices.
In a large heavy saucepan, iron skillet or Dutch oven, combine butter, sugar, syrup, and salt. Bring mixture to a boil over low heat, stirring until butter melts and sugar dissolves.
Reduce heat, add yams and baste them with the syrup. Cook, covered, over very low heat for 7-8 minutes. Turn yams, cover and cook another 7-8 minutes. Uncover, cook, basting occasionally for 15 minutes longer or until yams are tender and well glazed.