Crush the Oreo® Chocolate Sandwich Cookies (300 gram) in a food processor or put it in a Zip Loc bag, seal it up and bash it with something heavy like a rolling pin. Divide the crushed cookie mix into 3 portions. One cup of the cookie mixture will be put into the actual mousse cake mixture. A one-quarter cup is for sprinkling on top of the cake later. The remainder will be used for making the cookie crumb base.
Take the remainder, which is the largest portion of the crushed cookies and add Butter (50 gram) into it. Mix them together until it gains a wet-sand like consistency.
Grease a springform tin that's with a base that comes off, line it will some non-stick baking paper. Transfer the cookie mixture with butter in it into the tin. Use the base of a flat-bottom glass to press the cookie mixture down till it has a nice even layer. Put it in the fridge to chill for 20 minutes or until it's nice and firm.
Break up the White Chocolate (400 gram) into small pieces, and place them into a heat-proof glass bowl suspended over a little bit of simmering water in a saucepan. Use the water steam to melt the chocolate until it's nice and smooth. Then, take the bowl n the side and allow it to cool for about 10 minutes or so.
Put Cream (600 milliliter) into a mixing bowl and whisk it up until it's nice and thick. Pour in the cool and melted white chocolate and gently fold the cream and chocolate together until it's nicely combined. Add the crushed up cookies and fold them through so they are evenly distributed.
Gently spoon the cookie and cream mixture onto the cookie base. Smooth out the surface with a spatula just to make sure it's nice and even. Sprinkle over that reserved quarter cup of cookie crumbs
Place the cake in the fridge for about 5 to 6 hours or until it's nice and chilled. Transfer it to a plate. Serve and enjoy!