First make the dough. Put all the ingredients for the dough, except the egg, in the food processor and process until you have coarse crumbs. Add the egg and mix to a dough. Pour onto a piece of plastic wrap, press together and refrigerate for at least 30 minutes.
Meanwhile, preheat the oven to 180˚C (350˚F). Grease a 22cm (9 inch) diameter loose-bottomed cake pan with coconut oil. Press the dough into the pan in an even layer, pressing well around the edges. Punch holes in the bottom and bake in the oven for about 10 minutes.
Remove the pan from the oven and let the base cool while you make the filling. Mix all the filling ingredients together well with a whisk or mixer.
Pour the filling evenly onto the crust and return the pan to the oven. Bake the pie for about 45 minutes or until the filling is set.
Remove from the oven and allow to cool completely before removing from the pan. Sprinkle with the coarsely chopped walnuts and desiccated coconut before serving.