In 2-quart saucepan, heat butter and cocoa over medium heat, stirring frequently, until butter is melted and mixture is well blended. Remove from heat. Stir in graham cracker crumbs and powdered sugar. In bottom of ungreased 13x9-inch pan, press mixture to form crust.
Place heaping spoonfuls of ice cream on crust. With back of spoon, lightly press and smooth ice cream. Freeze 30 minutes.
Meanwhile, in 1-quart saucepan, heat chocolate chips and whipping cream over low heat 2 to 3 minutes, stirring constantly, until melted. Cool 15 minutes.
Drizzle chocolate mixture over ice cream. Arrange candies on top so each serving has 1 candy. Freeze until firm, about 2 hours. Let stand at room temperature 10 minutes before cutting into squares.