Place the 2 ounces malted milk balls in large resealable plastic bag and finely crush with rolling pin. Set aside.
For mousse, in small saucepan heat milk chocolate and bittersweet chocolate with 1/4 cup of the whipping cream over low heat until smooth, stirring constantly. Stir in malted milk powder, liqueur, and vanilla. Cool to room temperature.
In large chilled mixing bowl with chilled beaters beat 1-3/4 cups whipping cream to stiff peaks (peaks stand straight). Stir about 1/2 cup of the whipped cream into melted chocolate mixture; fold chocolate mixture back into remaining whipped cream. Fold in crushed malted milk balls. Spoon into 1-1/2- to 2-quart dish or 8 to 10 small bowls or glasses. Cover and refrigerate 1 to 24 hours.
In medium chilled bowl combine remaining 1 cup whipping cream, sugar, and cocoa powder; beat to soft peaks. Spoon on mousse. Top with malted milk balls. Makes 8 to 10 servings.