Add roasted broccoli to the pot, then pour in the vegetable broth and bring to a simmer. Let it cook for another 5 minutes.
Use an immersion blender or transfer the soup in batches to a blender, blending until smooth (or leave it slightly chunky for texture). Return the soup to the pot if using a blender.
Stir in milk and shredded cheddar cheese, cooking over low heat until cheese is fully melted and the soup is smooth and creamy.
Season with additional salt, pepper, and red pepper flakes to taste. Add a squeeze of fresh lemon juice for extra brightness if desired.
Serve hot, garnished with extra shredded cheese or fresh herbs if desired.
Notes
For a creamier texture, use half-and-half or heavy cream instead of milk.
Make it gluten-free by ensuring the vegetable broth is free from gluten.
Top with crispy bacon or croutons for added crunch.
This soup can be made ahead and stored in the refrigerator for up to 3 days, or frozen for up to 3 months.