Cook potatoes in boiling water to cover in a Dutch oven 30 to 40 minutes or until tender; drain. Let cool slightly. Peel potatoes, and place in a large bowl. Add 3 tablespoons butter, and mash. Add 3/4 cup sugar and next 6 ingredients; mash again, or beat at medium speed of an electric mixer until smooth. Spoon mixture into a lightly greased 2-quart casserole.
Combine brown sugar and remaining 4 ingredients; sprinkle over sweet potato mixture. Bake, uncovered, at 425° for 30 minutes or until thoroughly heated, shielding with aluminum foil after 20 minutes to prevent excessive browning.
Make-Ahead Directions: Prepare sweet potato mixture and spoon into greased casserole. Cover and chill overnight. Remove from refrigerator 30 minutes before baking; add brown sugar topping. Bake casserole as directed above.