Heat the oven to 170°C/Gas mark 3. Mix the biscuit crumbs and chocolate chips with the melted butter in a mixing bowl.
Press the mixture into a lightly greased 20cm spring-clip cake tin. Chill well.
In a separate bowl, whisk together the cream cheese, mascarpone, caster sugar, Vanilla Extract, eggs and cornflour until smooth, then pour into the tin and level. Bake for 50 mins-1 hr. Allow to cool.
To make the compote, put the blueberries, Ground Arrowroot, water, sugar and lemon juice into a small saucepan and bring to a simmer. Allow to thicken for a few minutes, and then cool in the fridge. Serve the compote poured over the cheesecake.