In large saucepan cook sweet potatoes in boiling salted water to cover. Simmer until tender, about 15 minutes; drain. Peel sweet potatoes and mash.
Stir in 2/3 cups brown sugar, butter, cinnamon, nutmeg and salt; mix well. Blend in milk.
Pour seasoned sweet potato mixture into buttered 1 1/2-quart casserole dish or buttered individual bakers. Sprinkle with remaining 2 tablespoons brown sugar. Bake in center of oven at 400, for 30 minutes or until heated through.