For the bavarois:
• 9 leaves gelatine
• 300 grams blackcurrents or boysenberries
• 2 tbsps crème de cassis
• 600 ml full-fat milk
• 8 free-range egg yolks
• 450 ml double cream
• 75 grams caster sugar
• 1 tbsp arrowroot
• 150 ml double cream
• 25 gm icing sugar
Preheat the oven to 220 C. Grease and line two 33x23 cm Swiss roll tins with baking parchment.
Whisk the eggs and sugar together in a large bowl until the mixture is light and frothy and the whisk leaves a trail when lifted out. Sift the flour into the mixture and carefully fold it in. Divide the mixture between the prepared tins and give it a gentle shake so that the mixture finds its own level, making sure that it has spread evenly to the corners.
Bake for 10-12 minutes, or until the sponges are golden-brown and begin to shrink from the edges of the tin. While the cakes are cooking, place two pieces of baking parchment a little bigger than the size of the tin on the work surface and sprinkle with caster sugar.
Turn the cakes out onto the sugared parchment and peel off the paper. Trim the edges of the sponges with a sharp knife and score 2 cm from the short edge, being careful not to cut right through.
Leave to cool slightly, then spread with jam and roll up cakes firmly from the scored end and set aside.
For the bavarois, soak the gelatine in cold water until soft. Puree the raspberries or boysenberries in a food processor and sieve to remove seeds. Stir the crème de cassis into the puree and set aside.
Pour the milk into a pan and heat until just under boiling point. Whisk the egg yolks and caster sugar together until pale and creamy. Pour the hot milk over the eggs and whisk together. Drain the gelatine, squeezing out any excess moisture and add it to the custard. Return the custard to the pan and cook until the mixture coats the back of a spoon. Do not boil, as this will split the custard and prevent the gelatine from setting. Remove from the heat, transfer to a clean bowl and leave to cool slightly before folding in the raspberry puree. Leave to cool for at least 30 minutes.
Meanwhile, line the base of a 2 litre round bowl with cling film, to help turn the Charlotte Royale out. Slice the Swiss rolls into 1.5 cm slices and use to line the base and sides of a bowl. Pack the slices closely together so that no filling can seep through, reserving enough slices to cover the top (which will become the base).
In a bowl, whip the cream until soft peaks form when the whisk is removed from the bowl, and stir into the bavarois. Spoon into the lined bowl.
Cover with the remaining cake slices. Cover with cling film and chill in the fridge overnight until set.
Turn out the Charlotte Royale onto a cooling rack.
To decorate, tip the caster sugar into a pan with 125 ml water and bring to the boil. Dissolve the arrowroot in two tablespoons of cold water and stir into the sugar syrup. Bring to the boil, remove from the heat and leave to cool slightly before spooning over the Charlotte Royale to glaze.
Dust with icing sugar before serving.