Wash and cut the beets in quarters, keeping the two colors apart.
To preserve the constrasting colors, place the beets into two different pans, one for the yellow ones, the other for the red ones. Cover with water, put the lid on and bring to a boil over high heat.
Reduce the heat to low and let the two pans simmer until the beets have the desired texture (20-30 minutes).
Drain the cooked beets and submerge them in cold water.
Peel the cooled down beets and cut them into cubes. Set aside.
Put all the dressing ingredients into the blender. Blend until the texture is smooth.
Blend the beets, the dressing and the chopped onion.