Rub the Fate Low Protein All-Purpose Mix and the margarine together in a mixing bowl until it resembles coarse breadcrumbs.
Add the water and combine to a dough and leave to rest for 10 minutes.
Dust a clean work surface with Fate Low Protein All-Purpose Mix and knead the pastry for a minute on the work surface until smooth.
Roll the pastry out between two pieces of grease proof paper, with a rolling pin to a 28cm circle and using the rolling pin, lift the pastry into the pie dish, making sure that you press the edges.
Cut the excess pastry off the sides
Meanwhile, in a pan boil the sweet potato for 10 minutes or until soft.
Drain the potatoes, add the butter and mash until smooth.
Add the Violife, red onion and salt and pepper to taste, mix until combined and spoon into the pastry case.
With the remaining pastry, roll between two pieces of greaseproof paper with a rolling pin to a 24cm circle.
Preheat oven to 190°C/fan 170°C/gas mark 5.
Using the rolling lift the pastry and lie on top of the sweet potato.
Crimp the edges of the pastry base and top together and using a fork prick the top.
Brush the top of the pie with ProZero and bake in the oven for 25 minutes.
Serve with onion gravy and vegetables for a hearty meal.
Add 1 tsp mustard powder to the mash for a kick!