Add the spinach in batches to a large hot frying pan and stir constantly for about 2 minutes. As each batch wilts,remove and place in a strainer,squeezing out the excess water with the back of a spoon.
Melt the butter in a pan. Add the onion and garlic and cook over low heat for about 8 minutes,or until soft. Add the spinach,salt and pepper and cook for 1 minute. Add the cream,simmer,and cook for about 2 minutes. Stir in the lemon juice.
In a blender or food processor,blend the mixture until fine and well combined. Check the seasoning,then serve.