Divide the broccoli up into florets. Peel the onion, cut it into small pieces and fry it in butter. Add the broccoli, broth and milk. Boil for 15 minutes.
Clean the leeks and cut them into round slices. Dice and fry the bacon, add the chopped parsley. Puree the broccoli in the broth, heat it and melt the processed cheese in it.
Add the leeks and let the soup just come to a boil. Serve the soup sprinkled with the bacon.