Whizz the ginger biscuits up in a food processor until they reach fine breadcrumbs.
With the mixer still running add the melted butter and salt and mix until the mixture resembles wet sand.
Tip the biscuit crumbs into a lined and greased 8 inch springform cake tin. Using a silicone spatula press the crumbs into an even layer at the bottom of the cake tin. Place in the freezer for 30 minutes to set.
Melt the white chocolate in a bain marie or a glass/metal bowl set over simmering water.
Once melted, turn off the heat and stir the cream cheese and mascarpone into the white chocolate.
Pour the mixture into a mixer to beat until smooth then add the vanilla extract and lemon juice.
Stir in the diced stem ginger.
Pour on top of the cheesecake base and place in the fridge overnight to set.
Remove the cheesecake from the springform tin carefully and peel off the greaseproof paper from the bottom. Place on a serving plate.
Whip the double cream with the icing sugar until it becomes thick enough to hold shape but not stiff. Pipe the double cream around the edges of the cheesecake.
Hold the white chocolate with one hand then using a vegetable peeler, peel the chocolate down lengthways at the side of the bar to create chocolate curls. Peel over a plate to catch the curls.
Decorate the cheesecake with the crystallised ginger and white chocolate curls.