Clean and wash the rhubarb and cut it into approx. 1⁄2 cm wide pieces. Boil up with 100 ml water and 50 g sugar in a pot and simmer for about 3 minutes. Let cool down.
Biscuits crumble. Divide into four glasses. Mix lemon juice and syrup, spread evenly on the cookie crumbs.
For the cream, soak gelatine in cold water for about 5 minutes. Finely puree half the rhubarb with a hand blender. Mix the soured milk, pureed rhubarb and 3 tbsp. sugar. Squeeze out the gelatine and dissolve it carefully in a small pot at low heat. First stir approx. 2 tbsp. thick milk cream into the gelatine, then stir into the rest of the cream. Chill for about 10 minutes until the cream starts to gel.
Whip the cream until stiff and fold into the gelling cream. Pour evenly into the four glasses, chill for about 2 1⁄2 hours. Spread the rest of the rhubarb on the cream.