1) Grind the chocolate cookies and add melted butter to them to make a coarse crumble.
2) Separate 3 eggs.
3) Whisk the egg white till hard peaks and keep aside.
4) Add the zest of one orange to yolks and whisk them in.
5) Over a double boiler, melt the chocolate mixed with the cream.
6) Once melted, add the yolks to the chocolate.
7) Slowly fold in the egg whites to make the mousse light and airy.
8) In a glass, spread the cookie crumb as the base and slowly pour the mousse on top.
9) Chill it completely in the fridge for 4-5 hours.
10) Garnish with chocolate flakes and chocolate zest.