1) Melt the butter in a medium saucepan, over medium heat. Add the onion and garlic and cook until translucent, about five minutes. Add the potato, thyme, salt, and and bring to a boil. Adjust the heat to maintain a gentle simmer, and cook uncovered until the potato is fork tender, about ten minutes. Add the broccoli and simmer for three minutes.
2) Puree the soup in batches in a blender or with an immersion blender. Return soup to the pot and add the cream. Bring to a simmer, taste, and season with salt and pepper.
3) Serve with optional toppings.