Preheat the oven to 200C/180C Fan/Gas 6. Line an 8" square pan.
Make the base by crushing the digestive biscuits and mixing with the melted butter. Press down to form an even layer in the pan. Bake 10 minutes.
Meanwhile make the cheesecake layer: combine all the ingredients with a spoon in a small bowl until thoroughly combined. Set aside.
Make the cookie layer: Beat together the butter and sugar in a large bowl/bowl of a stand mixer on a medium speed for 3-5 minutes. Add in the egg and vanilla and mix again.
Add the flour and chocolate chips to the cookie dough mix. Mix until totally combined.
Once the base has been baking 10 minutes, remove from the oven and pour over the cream cheese. Then use a spoon to 'dollop' the cookie dough over the cheesecake. Don't worry if it's not a perfect layer - it will spread while baking/cracks look good anyway!
Bake for 30-35 minutes, until golden. Let cool, then place in the fridge for 2+ hours before slicing!