Beat first 3 ingredients at high speed with an electric mixer until smooth and creamy. Add chocolate morsels; beat at lowest speed just until blended. Stir in chopped nuts.
Beat whipping cream at high speed with an electric mixer until foamy. Gradually add sugar, beating until stiff peaks form; fold into chocolate mixture. Pour into Chocolate-Macadamia Crumb Crust; freeze 8 hours. Garnish, if desired.