In a food processor mix together walnuts, cashew nuts, and dates.Process until combined, but still crumbly.
Press the mixture into the bottom of a 9 inch (23 cm) tart pan.
Add coconut milk, blueberries, agave syrup and arrowroot to a food processor or a high-speed blender and process until smooth.
Pour the mixture into a saucepan and bring to boil at medium heat, whisking constantly, until barely starts to bubble, for a few minutes.
Remove from heat and pour the mixture into your crust.
Let it cool and then place in the refrigerator for at least 4 hours to let it set.
Decorate your blueberry tart with blueberries and coconut chips (optional).