Lightly toasting the macadamia nuts brings out their rich, buttery flavor.
Preheat oven to 325°. Beat butter and cream cheese at medium speed with a heavy-duty electric stand mixer 2 to 3 minutes or until creamy. Gradually add sugar, beating at medium speed 5 to 7 minutes or until light and fluffy. Add eggs, 1 at a time, beating just until yellow disappears.
Add flour to butter mixture alternately with rum, beginning and ending with flour. Beat batter at low speed just until blended after each addition. Stir in vanilla and next 3 ingredients. Pour batter into a well-greased (with shortening) and floured 15-cup Bundt pan.
Bake at 325° for 1 hour and 10 minutes to 1 hour and 20 minutes or until a long wooden pick inserted in center comes out clean. Cool in pan on a wire rack 10 to 15 minutes; remove from pan to wire rack, and cool completely (about 2 hours). Spoon Snowy Rum Glaze over cooled cake.