A Charlotte royale is a combination of light sponge, fresh raspberry mousse studded with tiny strawberries, and whipped cream – exquisitely decorated of course!
Start by making the jam for the Swiss rolls. Put the prepared strawberries into a medium-sized pan with the sugar and cook gently over a low heat, stirring occasionally, until the sugar has melted. Bring the mixture to the boil and boil vigorously for about 4 minutes until the temperature reaches 104°C/219°F on the sugar thermometer, or setting point. Remove from the heat and whisk in the butter. Transfer to a heatproof bowl and leave to cool and set.
To make the sponges, heat your oven to 220°C/200°C fan/425°F/Gas 7. Put the eggs and sugar into a large bowl and whisk with an electric mixer until the mixture is light and frothy and it will make a ribbon trail on itself. Sift the flour over the mixture and carefully fold it in using a large metal spoon or plastic spatula.
Divide the mixture evenly between the 2 prepared tins. Give them a gentle shake so the mixture finds its own level; gently push the mixture into the corners if necessary. Place in the heated oven and bake for 10–12 minutes until the sponges are golden and starting to shrink away from the sides of the tin.
While the cakes are baking, lay 2 sheets of baking paper (cut a little larger than the tins) on the worktop and sprinkle them with caster sugar. As soon as the sponges are ready, turn them out onto the sugared paper and carefully peel off the lining paper. Trim the edges of the sponges with a sharp knife (this makes them easier to roll neatly) and score a line across each sponge 2cm in from one of the short edges (be careful not to cut right through). Leave the sponges to cool slightly before spreading the jam evenly over them. Roll up each sponge firmly from the scored end and set aside until needed.
To make the bavarois, soak the leaves of gelatine in a bowl of cold water for about 10 minutes until softened. Meanwhile, tip 450g of the raspberries into the bowl of a food processor and blitz to a puree. Pour into a sieve set over a mixing bowl and press the puree through the sieve to remove the seeds. Stir the framboise into the puree. Set aside until needed.
Pour the milk into a pan and heat to just under boiling point. While the milk is heating, whisk the egg yolks with the sugar in a heatproof bowl until pale and creamy. Pour the hot milk onto the yolk mixture in a slow steady stream, whisking constantly. Drain the gelatine and squeeze out all the excess water; then add to the bowl and whisk until melted. Pour the mixture back into the pan and cook gently, stirring constantly, until thickened enough to coat the back of the spoon and you can draw a line through with your finger (don't let the custard come to the boil or it will split). Pour the custard into a clean heatproof bowl and allow to cool slightly before folding in the raspberry puree. Leave to cool for at least 1 hour or until the custard has thickened to the consistency of thick, whipped cream.
Cut the Swiss rolls across into 1.5cm slices and use to line the base and sides of the clingfilm-lined bowl. Pack the slices close together so that very little of the filling will be able to seep through. Reserve enough slices to cover the top (which will become the base of the charlotte).
Whip the 300ml cream for the bavarois until it forms soft peaks. Gently fold into the raspberry bavarois mixture. Fold in the remaining 100g raspberries and the small strawberries, then spoon into the lined bowl. Cover the reserved slices of Swiss roll. Cover the bowl with clingfilm and chill overnight until set and firm.
To finish, turn out the charlotte onto a serving plate and peel off all the clingfilm. Put the caster sugar into a small pan, add the cold water and bring to the boil, stirring to make a light syrup. Mix the arrowroot with 2 tablespoons of cold water until smooth, then stir into the sugar syrup (it will thicken). Bring back to the boil, stirring, then immediately remove from the heat. Leave to cool slightly before spooning the sugar syrup over the charlotte to give an even, shiny glaze. Leave to set for about 5 minutes, then clean up the serving plate to remove any glaze.
Whip the cream with the icing sugar to soft-peak stage. Spoon it into a piping bag fitted with a star tube and pipe a continuous design of scallops around the base of the charlotte. Decorate with strawberries cut in fans.