Steam the 2 kg bag of frozen broccoli according to the package directions. A microwave steamer bag works well.
Allow the broccoli to cool slightly, then place it in a NutriBullet or blender. Blend until smooth and creamy.
Transfer the blended broccoli to a large soup pot.
Add the milk, butter, cream gluten free flour, salt, and whisk thoroughly until the flour is fully incorporated and there are no lumps.
Cook over low heat, stirring occasionally, until the soup is heated through and begins to gently simmer.
While the soup is cooking, steam the additional broccoli florets until tender.
Add the steamed broccoli florets to the soup and stir well.
Continue cooking on low heat for 20 minutes, stirring occasionally, until the soup starts to simmer.
Taste and adjust seasoning if needed before serving.