To a large bowl add dairy free butter, light brown sugar and granulated sugar and whisk with an electric whisk until creamy.
Add the egg and egg yolk and continue to whisk. Add the vanilla extract and whisk again until everything is combined.
Add the gluten free flour, xanthan gum, cornflour, bicarbonate of soda and salt. Mix well to form a dough.
Fold in the dairy free chocolate chips. Place the dough in the fridge for at least an hour (this will make the dough easier to handle for the next stage).
Line a standard loaf tin with baking paper. Remove the dough from the fridge and split into 3 equal sized pieces.
Press one third of the dough into the bottom of the lined loaf tin so that it fills the bottom of the tin. Press the second third of the dough around the outside of the tin, forming a pocket in the middle of the tin.
Fill the middle of the dough with chocolate spread (you may need to put the chocolate spread in the microwave for 20 seconds to make it easier to pour).
*Optional: You could also press any kind of chocolates or cookies into the chocolate middle. I've tried this recipe with both crushed up gluten free cookies and cream style biscuits and Nomo cookies and cream bunnies which both worked really well.
Place the tin in the freezer for 1 hour to firm up (the remaining cookie dough can be placed back in the fridge for now).
Remove the tin from the freezer and remove the remaining cookie dough from the fridge. Press the remaining dough on top of the chocolate centre to form a lid ensuring that it is completely covered and there are no gaps. Place back in the freezer for 30 minutes. Pre heat the oven to 180C.
After 30 minutes, remove from the freezer and bake in the oven for around 30 minutes. At this point you should have a nice golden top.
Remove from the oven and leave to cool completely in the tin. *Important step* Leave in the tin and place in the fridge for at least 4 hours, or ideally overnight. This gives the filling time to set (if you cut the cookie toast too early the filling will still be liquid.
Once completely cool carefully remove from the tin. Slice and enjoy!