Whisk the mascarpone and cream cheese and sugar until light and fluffy,
Whisk in the sour cream until combined, then add the eggs and whisk in one at a time, then add the vanilla bean paste and cornflour mixed with water, then fold in the stem ginger, ground ginger and lemon zest.
Pour the mixture into the base, Tap the tin to remove any air pockets. Cover the outside of the tin with two layers of tin foil and make sure it is tightly wrapped around the outside of the tin and place it in a large baking tray and place in oven, then carefully pour enough water into the tray to come half way up the tin, then bake for 65-85 minutes until set. there should be a slight jiggle when you move the tin. (if your oven has a tray type shelf then use that if you can't find a tray large enough to place your tin in)
Turn oven off and leave the cheesecake in the oven for 1 hour with the door slightly ajar
Remove from the oven and let cool on the side for 30 minutes. Mix the 150g sour cream and icing sugar for the topping together and spread onto the top before putting in the fridge for at least 3 hours or over night.
Once chilled remove from tin and place on a serving plate.