Measure out the butter, and set it aside to soften at room temperature.Line the base of a 15cm (6 inch) loose bottom or springform round cake tin with a piece of parchment, greasing the base first to stick down the parchment.In the bowl of your food processor, blitz the ginger biscuits until they break down into small crumbs.Add the butter, and continue blitzing until combined and the mixture resembles damp sand.Scoop this into the prepared cake tin, and use your fingers to press and compact it into a flat layer. Place it in the fridge to set whilst you prepare the filling.Preheat the oven to 170C (335F) / 150C Fan.Wipe the bowl and blade (carefully!) of your food processor clean of crumbs using some kitchen paper.Add the soft cheese and pumpkin to the food processor, and blitz together until combined. You may need to scrape down the sides a few times during this process.Add the sugar, and whilst blitzing again to combine, add the eggs, one at a time, down the feeding tube.Squeeze in some lemon juice, and continue blitzing until you have a smooth mixture. Don't worry if the mixture is looking really runny and thin - it will be delightfully fluffy when baked!Remove the cake tin from the fridge, and wrap the base three times securely with cling film (this is to prevent water seepage during the baking process).Then wrap the base in a double layer of aluminium foil, and sit the cake tin in a roasting pan.Carefully fill the cake tin with the cheesecake filling.Boil some water, and pour it into the roasting pan until it comes about halfway up the cake tin.Very carefully, transfer the roasting pan into the preheated oven on the middle rack, and bake for approximately 50 minutes.The cheesecake is done when it wobbles only slightly in the centre.Remove the roasting pan from the oven, place the cake tin on a cooling rack, and remove the foil. When it is cool enough, you can also remove the cling film.Leave the cheesecake to cool completely at room temperature before covering it with cling film and placing it in the fridge overnight to set.Gently remove the cheesecake from the tin, and sprinkle over some cinnamon or nutmeg before slicing and serving.