Add raisins, water, molasses, lemon juice, vanilla and salt to a large saucepan. Bring to the boil, lower the heat and simmer, uncovered, for 30 minutes.
Add walnuts, rum (if using) and nutmeg and stir to combine.
Mix the tapioca starch and water together and pour this into the pot while stirring constantly with a wooden spoon. Continue cooking until the mixture becomes thick.
Kill the heat, stir in ghee and set aside to cool for about an hour.
Preheat the oven to 375F. Grease a 9" pie plate with ghee and line with bottom pastry. Spoon in cooled raisin filling and cover with top crust or cut out shapes of your choice with a cookie cutter and place them randomly on top of the pie.
Beat the egg and coconut milk together and brush the top crust with this mixture.
Place the pie on the bottom rack of the oven and bake for 30 to 35 minutes or until the crust is nice and golden.