Clean the knotweed shoots and cut into pieces. Cook with the sugar on medium high heat until the stems have started to break down and are soft, about 15 minutes. The mixture should be thickened and you should be able to see the pan through the mixture when you drag a spoon through it.
Puree the knotweed in a blender until very smooth, then cool in a covered container and chill.
Bloom the gelatin in ice water until soft, then gently heat the knotweed puree and whisk in the gelatin until dissolved. Chill the mixture, whisk to relax the gelatin, then fold in the beaten egg whites and wild mint. Chill again, covered with plastic wrap until ready to use/serve.