The filling for this pie will take around 20 minutes to prepare before being cooked long and slow in the oven for around 2 hours 30mins. So you could make the filling first thing in the morning and even go out once its in the oven. After cooking, the filling needs to be thoroughly cooled, so leave plenty of time for this to happen. If you are making the pastry you will need 20 minutes for the pastry to chill in the fridge before rolling it out. Once the pie is assembled the whole thing goes back in the oven at a slightly higher temperature for around 45 minutes.