Preheat the oven to gas 4, 180°C, fan 160°C and line a loose-bottomed cake tin that has a good seal between the ring and the base.
In a saucepan, gently melt the butter. Mix in the crushed digestive biscuits. Use the mixture to line the base of the cake tin and press well all over to firm it down into the tin.
In a large bowl, put the sugar, eggs, vanilla, flour, cream cheese and sour cream. Mix using a spoon to begin with, then complete the mixing with a hand mixed to give a smoother, richer consistency.
While blending the mix, add in both the double cream and the condensed milk, if using. Add about 100-150g (3½-5oz) of the raspberries to the mix and gently blend them in. Pour and/or spoon the mix over the digestive base.
Put in the centre of the oven and bake for 35-40 minutes, until the top is a good golden brown. Turn the oven off, leaving the cake in it with the door open, for 15 minutes.
Take the cake out of the cooled oven and let it stand until completely cool. Place the cake (still in its tin) in the fridge and chill for about 24 hours to fully set the cheesecake.
Turn out of the tin. Dust the top with icing sugar to serve and dot with the remaining raspberries.
*Inspired by Anthony MacP. featured in the Realfood Cookbook
**This pudding is very rich and indulgent, so shouldn't be eaten too often. But it's perfect for those special occasions!