Preheat your oven to 350 degrees F.

First cook the cauliflower. In a pot of boiling water, boil the cauliflower pieces for about 3 minutes...you don't want them to cook fully, just until slightly tender. Drain well, and set aside.

Then make the roux: In a skillet over medium heat, melt the butter then stir in the flour. Cook for about 1 minute.

Slowly whisk in the whole milk, and stir until thickened. This should take about 4-5 minutes.

Season with salt, pepper and the dry mustard. Mix well.

Stir in the grated cheese until melted.

Add the cooked cauliflower pieces to a casserole dish, then pour on the cheese sauce.

Sprinkle the extra cheese over the top.

Bake for 40 - 45 minutes.

When done baking you may find the dish a bit watery, but just give it a good stir before serving and it will be nice and creamy.

Sprinkle on some chopped green onion, and serve.

Enjoy!