Mix the coconut flour with all the other ingredients up to and including the salt, mix by hand to form a dough. Transfer the dough to the prepared tin. Flatten the base by hand and create a rim of approx. 1.5 cm around the edge with your fingers. Place a sheet of baking paper over the base, weigh down with dried pulses (e.g. lentils).
To blind bake
Approx. 10 mins. in the lower half of an oven preheated to 180°C. Remove from the oven, leave to cool, remove the baking paper and pulses.
Bring the beetroot juice, orange juice and coconut milk to the boil. Using a whisk, stir in the cornflour, agar-agar and maple syrup, bring to the boil while stirring, simmer for approx. 1 min. Allow the filling to cool slightly, pour into the tart base, leave to cool.
Cover the tart and refrigerate overnight.
Slice off the top and bottom of the grapefruit and oranges, then peel all round the fruit down to the flesh. Using a sharp knife, cut out the segments between the white membranes. Decorate the tart with the fruit segments, sprinkle with pomegranate seeds.