Heat the oil in a large pan, add in the chicken and stir until slightly golden.
Add in the potato, carrot and zucchini before cooking these for a few minutes until slightly softened.
Add 1 cup stock to the pan and leave the chicken and vegetables to simmer.
Place the remaining stock and the cornflour into a separate bowl and stir until a paste is formed. Stir in the remaining stock and add to the simmering pan of chicken and vegetables.
Bring the mixture to a boil and then reduce the heat to medium-low.
Simmer for 5 minutes until the sauce is slightly thickened.
Stir through the parsley and tarragon and then pour the mixture into an ovenproof dish.
To make the pastry:
Sift the cornflour, rice flour, buckwheat flour and salt into a large bowl.
Add the Nuttelex, oil and use a knife to stir until a firm dough is formed. Use cold water if needed to help with this process!
Knead for around 3 minutes until the dough is smooth and shape into a ball.
To put the pie together:
Cover a flat surface with a light layer of flour and roll the pastry out.
Place the pastry over the pie filling, pinch the edges to seal, brush with egg and place into the oven for 35-40 minutes.
Leave to cool for a few minutes once removed from the oven as this will allow the pie filling to set a little.