Clean the onions and cut them in large pieces.
Boil the water and butter and homogenize with a food processor/blender.
Add the cut onions, a pinch of salt and the cloves. Cover with fat-free paper.
Allow to cook for 20 minutes. Then, blend the mixture with a cooking machine or thermoblender.
Season with salt. Press the cream through a sieve.
Allow to cool and keep in the fridge.