Wash the broccoli thoroughly under running water.
Chop the broccoli into small florets and set aside.
In a large pot, melt the butter over medium heat.
Add the chopped onion and sauté until translucent, about 5 minutes.
Stir in the minced garlic and cook for an additional minute.
Add the broccoli florets to the pot and stir well.
Pour in the vegetable broth, bringing the mixture to a boil.
Reduce the heat and simmer for about 10 minutes, or until the broccoli is tender.
Using an immersion blender, puree the soup until smooth.
Stir in the heavy cream and season with salt and pepper to taste.
If desired, add lemon juice for brightness and serve warm.