1. Crush the chocolate sandwich cookies into fine crumbs and mix them with the melted butter until evenly combined.

2. Divide the crumb mixture among 4 to 6 small dessert cups and press it gently into the bottom to form the crust. Chill for 10 minutes.

3. In a mixing bowl, beat the cream cheese, powdered sugar, vanilla extract, and salt until smooth.

4. In a separate bowl, whip the heavy cream to soft peaks, then divide it evenly into three portions.

5. Fold the melted milk chocolate into one-third of the cream cheese mixture, then gently fold in one portion of whipped cream until light and fluffy.

6. Spoon or pipe the milk chocolate mousse over the chilled crust and refrigerate the cups for 15 to 20 minutes.

7. Fold the melted white chocolate into another third of the cream cheese mixture, then gently fold in the second portion of whipped cream.

8. Add the white chocolate mousse layer over the milk chocolate layer and smooth the tops. Chill again for 15 to 20 minutes.

9. Fold the melted dark chocolate into the remaining cream cheese mixture, then gently fold in the last portion of whipped cream.

10. Spoon or pipe the dark chocolate mousse over the white chocolate layer and smooth the tops neatly.

11. Refrigerate the mousse cups for at least 4 hours, or until fully set.

12. Top with whipped cream and chocolate shavings just before serving.