Cut the broccoli into bite-sized pieces.
Finely chop the onion.
Melt the butter in a pot.
Sauté the onion until translucent.
Add the broccoli and stir-fry together.
Add the flour and stir-fry for 1 minute.
Pour in the milk and water and bring to a boil.
Boil until the broccoli is tender.
Add the cheese and let it melt.
Season with salt and pepper.