Beat whipping cream at medium-high speed with an electric mixer until soft peaks form. Fold in 2 to 3 tablespoons crème de menthe; set aside.
Unroll Chocolate Cake Rolls; brush each cake lightly with 3 tablespoons crème de menthe. Spread each cake evenly with whipped cream mixture. Reroll cakes without towels; place, seam sides down, on baking sheet. Cover and freeze at least 1 hour or up to 3 months.
Dust each cake evenly with cocoa, and cut into slices. Garnish, if desired, and serve with Chocolate-Mint Sauce.
* 1 1/2 teaspoons mint extract and 5 drops of green food coloring may be substituted. Omit brushing cake rolls.