Preheat oven to 180 °C. Line a large rectangle baking tray with baking paper. Set aside.
Once the pastry is chilled, roll out the pastry until 1 cm thick on a lightly floured surface. Place the rolled pastry onto the prepared baking tray.
To make tart filling, combine carrots, egg, coriander, cumin and pepper in a large bowl and stir to combine. Spread over the tart base. Spoon over the labne.
Fold pastry edges inwards and brush with milk before baking for 25 minutes in the oven, or until pastry is golden brown.
Top with coriander and walnuts before serving.