Here is the recipe you wanted from Josceline Dimbleby's Sweet Dreams book.
Christopher’s Bombe Surprise
Serves 8
2 large egg whites
Juice of 3 lemons
6 oz (175g) of caster sugar
1 teaspoon (5ml) of gelatine
1/2 pint (300ml) of whipping cream
6 oz (175g) plain chocolate, grated of chocolate curls
pinch of salt
Put egg whites in a bowl of a electric mixer and whip until stiff
Strain the lemon juice into a measuring jug and bring up to 5 fl oz (150 ml) - add water if necessary but if the lemons make up more than 5 fl oz (150 ml) it doesn’t matter
Put the lemon juice into a saucepan with the caster sugar and sprinkle on the gelatine
Dissolve the sugar and gelatine in the lemon juice over a low heat, then bring to the boil and bubble fiercely for 3 minutes.
Pour at once in a thin stream on to the egg whites, whisking all the time at high speed. Continue whisking for several minutes until cool and thick.
In another bowl, whisk the cream until thick, but not stiff, and then, using a spatula, fold gently but thoroughly into the egg white mixture. Transfer to a 2 pint (1.2 litre) metal basin or bombe mould, spreading the mixture up the sides with slight dip in the middle. Freeze for at least 5 hours.
When frozen, scoop out the centre of the ice cream and put aside in a bowl. Spoon the grated chocolate into the cavity, adding more if necessary to fill the gap completely. Stir around the reserved ice cream to soften a little and then spread back over the top of the chocolate.
Freeze thoroughly again, for at least 1 hour.
To unmould, dip the basin briefly in a sink of very hot water, loosen the top edges with a knife and turn out on to a serving plate.
Put back into the freezer until ready to serve