In a food processor, blitz roasted buckwheat, oat flakes, and salt until finely ground. Add coconut oil, maple syrup, and cashew butter, blending until dough-like. Press into tart tin and freeze for 30 minutes.

For the filling, separate seeds from passion fruits. In a blender, combine mango chunks, passion fruit juice, coconut milk, vanilla, and maple syrup. Blend until smooth.

Dissolve agar agar in mandarin juice in a small glass. Heat the mango mixture over medium heat until gently boiling, whisking in agar agar for 2-3 minutes.

Pour the filling over the crust, tap to remove air bubbles, and let it cool at room temperature for 10 minutes. Refrigerate for at least 1 hour to set.

Once set, slice the tart and garnish with passion fruit pulp and fresh mint.