Soak the gelatine in cold water. Peel the rhubarb and cut it into pieces. Vacuum seal the rhubarb with the liquids and the gelatine (without the water). Bake for 20 mins in a water bath at 80°C. If you do not have access to a vacuum machine you can let the rhubarb simmer in a saucepan instead.
Roll out the dough with the sugar thinly using a rolling pin. Bake for 40 mins between two silicone sheets in an oven at 160°C. Let the pastry cool and break it into pieces.
Make a light caramel of the sugar. Add the chocolate off the heat and stir vigorously until the sugar crystallizes and the chocolate crumbles. Pour the crumbles onto a silicone sheet to cool down. Crush into smaller pieces.
Soak the gelatine in cold water. Bring the water to a boil with chamomile and maple syrup. Cover with cling film and leave to infuse 10 minutes. Add the gelatin (without the water). Strain and pour into a siphon. Load with 2 gas cartridges, shake 40 times and leave to cool in the fridge. This recipe is hard to make without a siphon, but if you would still like to get the taste of chamomile you can let the chamomile infuse with the rhubarb instead.
Whisk egg yolk, sugar and corn starch in a bowl. Heat the milk with the vanilla and add it to the egg mixture. Stir until smooth and pour the mixture back into the saucepan. Boil for a few minutes while stirring. Strain the cream onto a silicone sheet, cover with cling film and cool. Whip the cream lightly. Stir the custard and fold it into the whipped cream. Pour the cream into a piping bag and keep in the fridge.
Bring the milk to a boil with sugar, glucose syrup and agar agar. Cool to room temperature and add the sourcream as well as the oxalis. Run in an ice cream machine.
Slice the rhubarb thinly on a mandoline and place in cold water. Pluck the oxalis, place the leaves on wet paper and cool in the fridge