Heat oven to 180°C (170°C for dark or nonstick pan). Generously grease and lightly flour tube cake pan, or spray with baking spray with flour.
In large bowl, mix cake mix, chocolate milk, butter, eggs and sour cream with spoon until well blended (batter will be very thick). Stir in chocolate chips. Spoon into pan.
Bake 56 to 64 minutes or until top springs back when touched lightly in center. Cool 10 minutes in pan. Turn pan upside down onto cooling rack or heatproof serving plate; remove pan. Cool completely, about 2 hours.
In 1-liter saucepan, heat glaze ingredients over low heat, stirring frequently, until chocolate chips are melted and mixture is smooth. Drizzle over cake. Store loosely covered.