In a large pot, melt the butter over medium heat. Add the chopped onion and sauté until translucent, about 5 minutes. Add the minced garlic and cook for an additional 1 minute until fragrant.

Add the broccoli florets to the pot and pour in the vegetable broth. Bring to a boil, then reduce the heat and let it simmer for about 10-15 minutes, or until the broccoli is tender.

Using an immersion blender, carefully blend the soup until smooth. If you don’t have an immersion blender, you can transfer the soup in batches to a regular blender.

Return the blended soup to the pot and stir in the heavy cream. Heat over low heat until warmed through, but do not let it boil.

Gradually add the grated cheddar cheese, stirring until melted and well combined. Season with salt, pepper, and lemon juice if using.

Serve hot, garnished with additional cheddar cheese or a sprinkle of black pepper if desired.