In a deep medium-sized saucepan heat olive oil over medium heat and add chopped onion, celery and thyme. Cook onions stirring often until they are transparent. Add the diced potatoes and 3 cups of water. Bring to a boil and simmer. Add the broccoli and continue to cook until broccoli is fork tender. Remove the saucepan from heat and cool for about 15 to 20 minutes. Ladle this mixture into the food processor or blender and process until fairly smooth. Mixture may be a bit granular but that is fine. Return the soup to the saucepan and place over low heat. Add lemon juice, sea salt and pepper. Stir well and heat through. Serve and sprinkle with parmesan cheese if desired. Makes 4 servings.