Heat oven to 350ºF. Grease bottom and side of springform pan, 9×3 or 10×2 3/4 inches, with shortening; lightly flour. In large bowl, mix flour, sugar, cocoa, baking soda and salt. Add water, oil, vinegar and vanilla. Stir vigorously about 1 minute or until well blended. Immediately pour into pan.
Bake 30 to 35 minutes or until toothpick inserted in center of cake comes out clean. Cool completely, about 1 hour.
Spread 1 cup fudge topping over cake; freeze about 1 hour or until topping is firm. In large bowl, mix ice cream and coarsely chopped candies; spread over cake. Freeze about 4 hours or until ice cream is firm.
In chilled medium bowl, beat whipping cream with electric mixer on high speed until stiff peaks form.
Remove side of pan; place cake on serving plate. Top with whipped cream. Melt 1/4 cup fudge topping; drizzle over whipped cream. Garnish with additional candies.