Put it into a small pot with the sugar, water, and vanilla and stir it together. Bring to the boil then reduce the heat and simmer for 8 mins until soft.
Transfer to a blender and whiz briefly until smooth but not frothy.
Video
Notes
When cutting rhubarb, make sure you wash it properly as dirt and impurities form on the outside. To make the rhubarb cook evenly together, make sure the pieces are all chopped roughly the same size.
The cooking time depends on how much water is in your rhubarb, but most are cooked down and soft in 10 minutes.
Make sure you cool the liquid slightly before blending to prevent the blender or food processor from creating pressure and spilling hot liquid.