Cut cake into 1/2-inch slices. Arrange cake slices, overlapping, in bottom of a 9-inch springform pan; set aside.
Combine coffee granules, hot water, and vanilla in a medium bowl; stir well. Stir in yogurt and crushed candy bars. Spread yogurt mixture over cake slices. Gently stir the Kahlúa into whipped topping, and spread over yogurt mixture. Cover and freeze for 8 hours or until firm.