Preheat the oven to 160°C. Line the bottom of a 20cm springform tin.
Blitz the digestive biscuit in a food processor until it forms fine crumb, fold in the melted butter until it is evenly coated. Press the biscuit base into the bottom of the springform tin. Bake in the oven for 10 minutes.
Meanwhile in a bowl, cream together the cream cheese, caster sugar and sour cream. Add in the eggs and orange oil, whisk until it is all combined together. Finally sieve and whisk through the flour.
Pour the mixture on top of the base and place in th oven for 1 hour until it is set. Then turn the oven off and leave the cheesecake to cool in the oven for the next 1 hour before removing and allowing to cool on the side. Once cool, place in the fridge for 4 hours to firm up.
To make the mixed berry coulis, place the caster sugar with 200g of the mixed berries in a saucepan on a low heat until they soften fully. Then place in a blender and blitz until a puree. Pour back in the pan with the remaining mixed berries and cook for a minute until they soften slightly.
Slice the cheesecake and pour over the mixed berry coulis to serve.