First make the Oreo crust. Place the whole Oreos in a freezer bag and crush with a rolling pin or with the bottom of a glass bowl until they are in crumbs.
Melt the butter and stir it through the Oreo crumbs.
Using your hands, press the Oreo crumbs into the tart tin to form a shell. Press up the edges to form the sides of the shell and make the centre of the shell as smooth and uniform as possible.
Chill in the fridge for an hour.
Make the lime curd. Put the eggs, butter, lime juice, zest and sugar in a glass bowl. Microwave on high for 4 minutes, 1 minute at a time, stirring well after each minute. Then microwave on high for 30 seconds three times, again stirring well after each period is up. The curd should thicken so it coats the back of a spoon.
Once it has thickened, set it aside to cool. Once the Oreo crust has chilled for an hour, pour the curd on top and then chill it for another hour.
When the hour is nearly up, make the white chocolate ganache filling. Heat the cream and pour it over the white chocolate in a bowl. If it does not melt fully put the bowl on top of a pan of hot water and stir until fully melted.
Stir through the lime zest and lemon extract then pour the ganache into the tart. Chill for another hour.
To decorate, melt the dark chocolate and drizzle over the top. Serve chilled.