Add the gluten free flour and salt to a large mixing bowl and combine. Add the diced chilled butter and work in gently with a fork. Bring together with as much cold water as you need to form a dough.
Transfer the dough into a piece of plastic wrap and chill for 30 minutes. Roll out between two pieces of cling film and transfer to line your pie dish.
For the filling
Boil the sweet potato whole in skin for 40 to 50 minutes until soft. Run cold water over the sweet potato, and remove the skin.
Preheat oven to 180 C.
Break apart the sweet potato in a bowl. Add the butter, and mix well with mixer. Stir in sugar, milk, eggs, mixed spice, cinnamon and vanilla. Beat on medium speed until mixture is smooth. Pour filling into prepared pastry base.
Bake in the preheated oven for 55 to 60 minutes, or until knife inserted in centre comes out clean. Serve with a dollop of cream.