To make the raspberry mousse, soak the gelatine in a bowl of cold water.
Whip the cream to soft peak and put in the fridge to chill.
Put 75g of the raspberry puree in a saucepan with the sugar, bring it to a boil and then stir in the gelatine until it has dissolved, add the warm puree to the remaining puree and stir to mix. Fold in the whipped cream until it is completely combined, then place the mousse in the hemisphere moulds and put on a tray and place them in the freezer.
To make the dacquoise, preheat the oven to 170C Fan, line a baking tray that is at least 20cm x 30cm with baking parchment.
Whip the egg whites in the bowl of stand mixer until they hold a soft peak, add the caster sugar and whisk until firm and glossy.
Gently fold in the ground almonds, raspberry powder and rose extract until it is evenly mixed.
Spoon the cake batter in a piping bag fitted with a 1cm nozzle. Pipe neat rows on the prepared baking sheet and bake it for 15-20 minutes until it is golden. Leave to cool in the tray.
To make the bavaroise soak the gelatine in a bowl of cold water, for a few minutes until soft.
Put the white chocolate in a bowl and make sure it's broken into small pieces.
Place the egg yolks and sugar in a small bowl and mix until light in colour.
Heat the milk and bring it to a boil, pour half of the milk on the egg mixture and then return it all back to the pan and heat gently to 84C. Remove the excess watch from the soaked gelatine and add to the milk mixture, stir until dissolved. Strain this liquid over the chocolate and mix until the chocolate is melted. Leave to cool and semi-whip the cream, add this to the chocolate and use immediately.
To assemble, use a cake tin that is bigger than the entremet ring and place a piece of greaseproof paper inside it. cut out a circle of the dacquoise with the entremet mould and place it in the bottom of the entremet ring. inside the larger cake tin.
Spoon a small amount of the white chocolate bavaroise in the bottom of the mould and spread it around evenly using a stepped palette knife.
Take the raspberry mousse that is frozen in the moulds and place them in a ring inside the entremet mould, place them about 2cm from the edge. Spoon the rest of the bavaroise over the top and flatten it with a stepped palatte knife, ensure it's as smooth as you can make it.
Place the entremet in the freezer for at least 4 hours, in the meantime take the rhubarb and cut it into strips, using a 2cm cookie cutter, stamp out circles of rhubarb, this is quite fiddly so take your time.
You want the circles to be around 2-3mm thick, so once you have stamped out the circles you may need to slice them again to be thinner.
Place the sugar and water in a saucepan and bring it to a boil. Add the rhubarb pieces and cook for around 30 seconds. remove the rhubarb with a slotted spoon and place on a silicone mat or use kitchen towel.
Remove the entremet from the freezer and using a chef's blowtorch heat the mould and slide it off gently.
Place the small rhubarb circles on top of the entremet and overlap them where necessary. You can also use strips of rhubarb to wrap the side of the cake if you want to cover the visible layer of dacquoise.
Leave to thaw and then slice to serve.