put the two cup malted milk balls in a resealable plastic bag; seal bag. Using a rolling pin, finely crush malted milk balls; set aside.
In a small pan mix 1/4 cup of the cream, the milk chocolate, and bittersweet chocolate. Cook and stir over low heat until chocolate is melted. Stir in malted milk powder, liqueur, and vanilla. Cool to room temperature.
In large bowl beat 1 3/4 cups of the cream with electric mixer on medium to high speed until stiff peaks form. Tips stand straight. Stir about 1/2 cup of the whipped cream into chocolate mixture to lighten. Gently fold chocolate mixture into remaining whipped cream. Gently fold in crushed malted milk balls. Transfer to 8 to 10 small dessert dishes or glasses or a 1 1/2 to 2 quart serving bowl. Cover and chill for 1 to 24 hours.
Before serving, in medium bowl mix remaining 1 cup cream, sugar, and cocoa powder. Beat on medium speed until soft peaks form, tips curl. Spoon on top of mousse. If desired, garnish with additional chopped milk balls. Makes 8 to 10 servings