Preheat oven to 350 degrees.
Grease and flour a 12 cup fluted tube pan.
In large bowl, blend cake mix, cinnamon, nutmeg, potatoes, 1/2 c butter, water, and eggs until moistened.
Beat 2 minutes at highest speed.
Pour into prepared pan.
Bake 40 - 50 minutes.
Cool upright in pan 25 minutes.
Invert onto serving plate.
Cool completely.
In a small saucepan, blend chocolate chips, 1 T butter, and milk over low heat until chocolate melts, stirring constantly.
Remove from heat; stir in powdered sugar until smooth.
Spoon over top of cake, allowing some to run down the sides.