For 4-6 servings:
Brush the cake tin lightly with some melted butter and lightly flour. Preparing the chestnuts with a small sharp pointed knife, make a two slits on the flat side of the chestnuts in a cross formation. Either place in a roasting tray on into a very hot oven for 10- 15 minutes or wrap well in tin foil and place in the fire for 5 minutes (if you are roasting them to eat as is, add some salt into the parcel). Remove from the heat and allow to cool slightly and peel. The chestnuts must still be hot to warm while peeling, if allowed to cool too much they will be difficult to peel
Place the peeled chestnuts in the milk with a little extra sugar, bring to a boil and simmer for approximately 15 minutes until soft. Drain and puree the chestnuts in a food processor. Place the sugar and eggs in a bowl and whisk until thickened. Add the melted butter and combine. Add the chopped almonds, chocolate, zest and juice of the lemon and the brandy and combine. Whisk the egg whites to the stiff peak stage and fold gently into the above misture. Pour into the prepared cake tin and bake in the middle of the oven: pre-heated to 180ºC for 45 minutes.