1Place sweet potatoes in 3-quart saucepan; add enough water to cover. Cover and heat to boiling; reduce heat. Simmer covered 20 to 25 minutes or until tender; drain. Shake potatoes in saucepan over low heat to dry.
2Heat oven to 350ºF. Mash potatoes with 2 tablespoons butter and the salt until no lumps remain. Spoon into ungreased 1-quart casserole. Mix remaining ingredients; sprinkle over potatoes.
3Bake uncovered about 30 minutes or until heated through and streusel mixture is golden brown.