First make the ice cream. Zest two of the seville oranges and then put the juice from all 3 of them into a bowl, removing the pips. Stir in the icing sugar until it dissolves completely. Pour the cream and whisk until it holds soft peaks. Pour into steeple shaped containers (or just into a freezer container for scooping) and cover.
Place in the freezer for at least 3-5 hours.
For the marquise, break the chocolate into pieces and place in a heatproof bowl over a saucepan of simmering water until it has almost melted. Add in the butter and stir until they are fully blended and there are no lumps. Remove from the heat and whisk in the egg yolks one by one.
Whip the cream until it is just thick, and stir into the chocolate mixture and stir in the brandy. Whisk the egg whites until light and fluffy and gradually add the sugar, whisking all the time. Fold the eggs whites into the chocolate mixture.
Line a 2-pint loaf tin with a couple of layers of Clingfilm and pour the chocolate mixture in, fold over the Clingfilm to cover the surface and place the marquise in the freezer for 6-8 hours.
Cut a slice of marquise and place on a dish and put a ‘steeple’ of ice cream on top (or alternatively just place a scoop on top).