In a large pot, heat a drizzle of olive oil over medium heat. Add chopped broccoli, diced celery, and parsley, stirring them gently for about 2 minutes until the vegetables become vibrant and aromatic.

Pour in the vegetable broth, stirring gently to combine. Increase the heat until the broth comes to a rolling boil, then reduce the heat to a simmer. Cover and cook for approximately 15 minutes.

Once the vegetables are tender, remove the pot from heat and let cool. Using an immersion blender, puree until desired consistency.

Return the blended soup to the pot over low heat. Taste and adjust the seasoning with salt, pepper, and lemon juice if desired.