Cookie Crust:
Place the vegan cookies in a food processor and blend them into fine crumbs. Alternatively, place them in a freezer bag and crush them with a rolling pin.
Transfer the cookie crumbs to a bowl, add the melted vegan butter, and mix until fully combined.
Press the mixture evenly into a 9-inch tart pan (or another pan with a removable bottom).
Place the tart pan in the freezer for 15 minutes, or in the refrigerator for 30 minutes, to allow the crust to solidify. You can also pre-bake the crust (see notes).
Lime Layer:
5. In a saucepan, combine the coconut milk and agar powder, stirring until the agar is fully dissolved.
6. Bring the mixture to a boil and cook for 1-2 minutes, stirring constantly, until thickened (follow package instructions if needed).
7. Turn off the heat and stir in the agave syrup and freshly squeezed lime juice. Let the mixture cool slightly.
8. Pour the lime mixture onto the chilled cookie crust and refrigerate for about 1 hour, or until the top is set.
Blue Layer:
9. In a small cup, dissolve the spirulina powder in the water and set aside.
10. In a saucepan, stir together the coconut milk and agar powder until the agar is fully dissolved.
11. Bring the mixture to a boil and cook for 1-2 minutes, stirring constantly. Turn off the heat and stir in the agave syrup, vanilla extract (if using), and the spirulina mixture.
12. Carefully pour the blue layer over the set lime layer and refrigerate for another 2 hours, or until the tart is fully firm.
To Serve:
13. Once the tart has set, gently remove it from the pan by pressing against the removable bottom.
14. Garnish with fresh blueberries, blackberries, and lime slices. Enjoy!