Add the roasted buckwheat to your food processor and blitz for a couple of minutes until roughly ground.
Add the cashews and blitz for another minute or so until the texture resembles a light crumb consistency.
Add the remaining base ingredients and continue to process until all the ingredients start to stick together to form a dough consistency.
Press the mixture evenly into your tart tin, making sure all the edges are evenly covered.
Set the base aside in the freezer to set.
Meanwhile add all the filling ingredients to your blender and blitz until completely smooth and creamy.
Remove the tart base from the freezer and fill with the key lime mixture (saving a cup for decorative piping).
Add the remainder of the filling to a piping bag and pipe your desired design on top of the tart.
Place the tart in the freezer to set for 6 hours.
Meanwhile prepare the meringues by preheating your oven to 100° C.
Add the aquafaba to a large bowl and beat using an electric whisk for a couple of minutes.
Add the sugar and vanilla extract and whisk for a further 10 minutes until the mixture forms stiff glossy peaks.
Line a baking tray with parchment paper and use a piping bag to pipe out the mixture into miniature meringues.
Bake in the oven for 1.5 to 2 hours before removing from the oven and allowing to cool completely before use. (hold aside some meringues for decorating the tart, any others can be stored at room temperature in an airtight container).
Once set, remove the tart from the tin and allow to defrost for one hour.
Decorate with mini meringues, lime rind and thyme leaves.