2) In a bowl, stir the digestive biscuit crumbs and 50g of the brown sugar until well combined. Add the butter and mix until the crumbs are evenly moistened. Press firmly and evenly on the bottom and sides of a 23cm tart dish to create a crust, being sure there are no cracks. Bake in the oven for 10 minutes or until golden. Remove from the oven.
3) Meanwhile, make the filling. Unwrap the potatoes and peel them. Put the flesh into a bowl and mash well with a fork. Add the eggs, 90g of the brown sugar, the cream, flour, cinnamon, nutmeg and vanilla and whip until very smooth with a whisk. Pour the filling into the partially baked shell. Sprinkle the remaining brown sugar over top and bake in the centre of the oven until set, about 40 minutes.
4) Allow the pie to cool completely before cutting. Serve at room temperature.