MICROWAVE chocolate with 1 cup of the whipping cream on MEDIUM power for 3 min.; stir until chocolate is melted. Stir in coffee mix. Cool for 15 min.
WHIP remaining 1 cup whipping cream until soft peaks form; gently fold into chocolate mixture.
SPREAD 1/4 of the mousse onto bottom of 9-inch springform pan. Layer 15 chocolate wafers over mousse. Repeat layers 2 more times, ending with a layer of mousse.
FREEZE for 4 hours or overnight. Let stand for 30 min. at room temperature before serving. Garnish with drizzled chocolate if desired.