To Prepare the Pistachios:
Soak the pistachios in a large bowl covered with water, refrigerating overnight (or for at least 6 hours).
Rinse the soaked pistachios and remove as many of the skins as possible by rubbing them with your fingers.
For the Crust:
Add the roasted buckwheat, oat flakes, cacao powder, and salt to a food processor. Process until you get a fine crumb texture.
Add the medjool dates, coconut oil, and maple syrup. Continue processing until the ingredients form a sticky, dough-like consistency. If the mixture is too dry, add a teaspoon or two of water until it holds together when pressed.
Line the base of a 9-inch springform tin with parchment paper. Press the dough evenly into the base and up the sides of the tin, smoothing it with a spatula or the bottom of a glass. Trim the edges for a neat finish.
Place the crust in the freezer to set while preparing the filling.
For the Filling:
In a high-speed blender, combine the soaked pistachios, chilled coconut milk (only the thick part), vanilla soya yogurt, maple syrup, coconut oil, and almond extract. Blend until completely smooth and creamy.
Pour the filling into the prepared crust. Tap the tin gently on the counter to remove any air bubbles.
Freeze the tart for 2-3 hours until fully set.
To Decorate and Serve:
Once set, carefully remove the tart from the springform tin while it’s still frozen.
Decorate the top with chopped pistachios, dark chocolate, and dried rose petals.
Allow the tart to defrost for 30-40 minutes before serving.