Lightly grease an 20cm / 8 inch pie dish (or quiche tin) with oil. (I use a loose-bottomed tin for easy removal).
Prepare the pastry: Place the flour, coconut cooking butter (or dairy-free spread), sugar and salt in a food processor. Whiz until combined. While the machine is running, add orange juice a little at a time until the mixture starts to come together (I find I need about 3½-4 TBSP when using coconut butter and 2½ TBSP when using dairy-free spread). Scoop the mixture into a ball. Wrap in cling film (plastic wrap) and chill for 15-20 minutes.
Once the pastry has rested, place it on a lightly floured pastry mat and lay the cling film (plastic wrap) on top. Roll out the pastry into a circle large enough to fill the tin and the sides. Place the pastry in the tin and press it into the edges and up the sides. Slice off any excess pastry. If you have any holes in the pastry, you can patch it up using the scraps.
While the pastry is resting, prepare the filling. First, make the flax ‘egg’. Place the ground linseed in a small bowl with 90ml / 6 TBSP warm water. Whisk together with a fork then set aside for 10 minutes to gel up.
Set aside half of the pecan halves for decorating the top of the pie. Roughly chop the remaining pecans.
Preheat the oven to 190C (170C fan) / 375F.
Place the coconut oil, maple syrup, coconut sugar, vanilla extract and pinch of salt in a small saucepan over very low heat. As the oil melts, whisk to combine. When fully melted, remove from the heat.
In a small bowl, whisk together the milk, flour and corn flour until smooth. Pour it into the pan. Add the flax ‘egg’ and whisk until fully combined. Stir in the chopped pecans. Pour the mixture onto the pie crust (it will be very runny, but this is normal). Arrange the pecan halves on top.
Carefully place the pie on a baking sheet in the centre of the oven. Bake for 20 minutes at 190C (170C fan) / 375F. Reduce the heat to 130C (130C fan also) / 275F and bake for a further 40 minutes. Remove from the oven and leave to cool completely. (It will firm up as it cools).