In a large pot warm the olive oil and start cooking the diced onion, chopped head of celery, diced carrot, potato, and minced garlic cloves. Stir in the broccoli florets as well.
Season with salt and pepper to taste and stir in the vegetable broth, mustard, and bring the mixture to a boil. Cook for 10 minutes.
With the help of a high-speed blender puree the whole veggies and bring them again to medium heat.
Stir in the sour cream and cook for 2-3 minutes.
Serve the soup in a serving bowl and garnish with olive oil, baked croutons, and baked broccoli florets.