Prepare the raspberry jelly: Remove the stalks from the raspberries and strawberries and roughly chop. Place in a bowl with the sugar, mix together and cover with cling-film. Set the bowl over a pot of simmering water on a low heat and leave for 1 hour until the berries have released all their juice. Remove the bowl from the heat and refrigerate for 1 hour. Pass the juice through a double-layer of muslin cloth and discard the pulp.
Soak the gelatine in cold water until soft. Gently heat 50ml berry juice in a small saucepan. Squeeze the water from the gelatine, add to the berry juice and stir until dissolved. Stir into the remaining berry juice. Line a small shallow tray with cling-film and pour the jelly into it to a height of 1cm. Refrigerate the jelly for 4 hours until set.
Prepare the Chiboust: Whip the cream to ribbon stage and refrigerate until ready to use. Soak the gelatine leaves in cold water and when soft, squeeze dry.
Bring the champagne to the boil in a heavy-based saucepan. Remove from the heat, pour 50ml champagne into a separate saucepan and add the gelatine. Reduce the heat, stir in the gelatine until it has dissolved and keep in a warm place until ready to use.
Whisk together 100g sugar and the egg yolks in a bowl until pale and doubled in volume. Add the remaining 200ml champagne onto the egg yolk mix. Cook over a very low heat in a heavy-based saucepan. Stir continuously with a wooden spoon for 10 to 12 minutes until the custard coats the back of a wooden spoon. When cooked, add the remaining champagne and gelatine and stir well. Remove from the heat and pass through a fine sieve.
Place the remaining 190g sugar and 20ml water in a heavy-based saucepan and heat to 121°C. (Use a sugar thermometer to gauge the temperature).
Place the egg whites and icing sugar in an electric mixing bowl and whisk the egg whites to a firm peak. Reduce the speed, slowly pour in the 121°C sugar syrup and continue to whisk until fully incorporated. Remove from the machine and fold the egg and champagne-mix through the meringue, followed by the whipped cream. Pour the Chiboust into 100ml dariole moulds and refrigerate for 2 hours until set.
Turn out the jelly onto a clean chopping board and cut out rounds using a 1cm round pastry cutter to make small cylinders of jelly. Run the tip of a knife around the inside of the Chiboust and invert into the centre of a plate. Surround the Chiboust with the jelly cylinders and fresh raspberries. Fill a plastic squeeze bottle with raspberry coulis and pipe small dots of the coulis between the jelly and raspberries.