Start by rinsing your rhubarb stalks. Young, thin stalks do not need to be peeled. If you have old thick wooden ones take out the outer layer. Cut them to 1 cm pieces.
Boil your water and add the rhubarb and sugar. Boil the rhubarbs for 10 minutes until they are soft and mushy.
Mix your starch with the water and pour it into the rhubarb soup while you are constantly stirring.
If you use potato starch, let the soup just bring to a boil so it thickens. If you use cornstarch then you need to boil the soup for 2-3 minutes. Remember to stir it constantly after adding the starch. Otherwise, clumps will form.
Pour your hot rhubarb soup into a serving jar. (one that tolerates heat). Sprinkle some sugar on top to prevent a skin to form on top.
Let it cool down and serve with whipped cream, vanilla sauce or whole milk.
Notes
Nutrition per serving: 80 calories, 0 g fat, 18,5 g carbs, 0,6 g fiber, 0,3 g protein.