Preheat your oven to 175°C (350°F). Lightly grease the base and sides of a 9.5" tart tin with some oil or vegan butter.
Make a "flax egg" by mixing together the ground flaxseed with 2½ tablespoons of water. Allow it to sit for 5 minutes.
In your food processor, combine the flax egg, gluten-free flour, ground almonds, coconut sugar, salt, and vegan butter and blend until the ingredients stick together to form a dough. If needed, add the tablespoon of water and blend again to bring the mixture together.
Evenly press the dough half of the dough into the sides of the tart tin first, then press the remaining dough into the base of the tin. With a fork, gently prick the dough several times.
Bake the crust for 12-15 minutes until slightly browned, then allow to cool to room temperature (do not remove the tart from the tin). Once at room temperature, place the tart in the fridge to chill while you prepare the filling.
Filling
If using fresh passion fruit, scoop the flesh and pass it through a sieve to separate out the seeds. Use the back of a spoon to press and squeeze out all of the pulp.
Add the passionfruit pulp, orange juice, and light brown sugar to a saucepan and simmer on medium heat for 10 minutes.
In a bowl, whisk together the plant-based milk, cornflour, and agar-agar to remove any lumps. Add the cornflour mix to the saucepan and simmer for another 3 minutes, whilst whisking vigorously. Add the coconut cream and continue to simmer for another minute while whisking vigorously. Remove from the heat and allow to cool slightly for 10 minutes before pouring the filling into the tart shell.
Place in the fridge to set for 3-4 hours (or overnight if preferred).
Garnish with whipped coconut cream and passionfruit pulp or passionfruit coulis.
Storage
Store in an airtight container in the fridge and consume within 2-3 days.