PREHEAT oven to 350° F. Grease 10-inch bundt pan.
MICROWAVE 1 1/3 cups morsels in uncovered microwave-safe bowl on MEDIUM-HIGH (70%) power for 1 minute; STIR. The morsels may retain some of their original shape. If necessary, microwave at additional 10- to 15-second intervals, stirring until melted. Cool to room temperature.
COMBINE cake mix, eggs, sour cream, milk, rum, butter and melted morsels in large mixer bowl. Beat on low speed just until moistened. Beat on high speed for 2 minutes. Stir in 1 cup nuts. Pour into prepared bundt pan.
BAKE for 50 to 60 minutes or until wooden pick inserted in cake comes out clean. Cool in pan on wire rack for 20 minutes. Invert onto wire rack to cool completely; transfer to serving platter. Pour Glaze over cake; sprinkle with chopped nuts.
MICROWAVE remaining morsels and 1 to 2 tablespoons milk in small, uncovered, microwave-safe bowl on MEDIUM-HIGH (70%) power for 30 seconds; STIR. If necessary, microwave at additional 10- to 15-second intervals, stirring until smooth. Cool for 5 to 10 minutes.