Mix all dry ingredients together: ground almonds, coconut flour, baking soda and salt.
Mix in butter with hands to dry ingredients.
Mix in most of the egg, saving 1-2 tsps for glazing the pastry before baking.
Place in fridge to firm up.
Filling
Add the butter to the pan and slowly fry onions on a low heat.
Add in the leeks, when they are half cooked add the mushrooms and garlic. Fry until cooked.
Sprinkle with chickpea flour.
Slowly add in chicken stock and stir to thicken. Season with salt and pepper.
Season with salt, pepper and dijon mustard.
Pour into cooking dish and add in pieces of cooked chicken.
Combine
Preheat oven to 180°C.
Using a rolling pin and two pieces of greaseproof paper roll the pastry out to desired shape.
Place on top of filling and fold in the edges to form a crust. You can use the edge of spoon to create a crimped edge. And if desired make any decoration you like.
Brush the remaining egg over the top of the pastry.
Bake in the oven for 20 minutes until the pastry looks golden.