Place 13x9-inch pan in freezer. Let ice cream stand at room temperature 15 minutes to soften. Line cold pan with plastic wrap. Spoon ice cream into pan; cover with another sheet of plastic wrap. Spread ice cream to even thickness. Freeze 1 hour. Heat oven to 350°F. Spray a second 13x9-inch pan with cooking spray. Make and bake cake mix as directed on box for 13x9- inch pan, using water, oil and eggs. Cool 10 minutes; remove from pan to cooling rack. Cool completely.
Cut cake horizontally to make 3 layers; split layers in half to make 6 total. Press 1 layer in bottom of 9x5-inch loaf pan. Remove ice cream from freezer; carefully lift ice cream from pan and remove plastic. Place 1 ice cream layer on cake in pan; top with second cake layer. Repeat layers. Return to freezer. Repeat for second cake. In large bowl, beat whipping cream and powdered sugar with electric mixer on high speed until stiff peaks form. Spread whipped cream over cake. Serve, or freeze up to 8 hours. Before serving, sprinkle cake with crushed candies.