Fill a large stock pot with enough water to cover the vegetables. Bring the water to the boil.
Add the diced potato, broccoli heads, celery and salt to the pan to cook for about 5 minutes or until the stalk is tender when pierced with a sharp knife and the potatoes are cooked.
Use a slotted spoon and/or tongs to remove the vegetables from the water and transfer to a blender.
Pour enough water into the blender to start the blending process and continue to add water, a little at a time, until you reach a thick soup consistency.
Add the lemon juice and pepper to taste and serve immediately.
Serve with a spoon of Greek yoghurt and chopped herbs