Heat olive oil in a large pot over medium heat.
Add chopped onion and sauté until translucent.
Stir in minced garlic and cook until fragrant.
Add broccoli florets and vegetable broth to the pot.
Bring to a boil, then reduce heat and simmer for 15 minutes.
Remove from heat and let cool slightly.
Use an immersion blender to puree the soup until smooth.
Stir in heavy cream and season with salt and pepper.
Heat gently without boiling, stirring until warm.
Serve hot, garnished with croutons or cheese if desired.