Prepare Cauliflower:.

Mix oil, rosemary, salt, pepper and garlic together.

Mix with cauliflower and place in a large casserole dish in one layer.

Roast in a preheated oven at 450 degrees for 20 minutes; give a toss and bake for 10 more minutes.

Sauce:.

Place the butter and flour into a microwave safe glass container whisk to incorporate.

Whisk in the milk and continue stirring until the sauce is thickened about 3 minutes. If the sauce is very thick add a little more milk, the sauce should be thick but still runny. Add the grated cheese and stir until melted.

Place the florets in a greased 9 x 13 baking dish.

Pour the thickened cheese sauce over the cauliflower ensuring all the florets are covered. Sprinkle with grated cheese and a good twist of black pepper.

Bake in the hot oven until the sauce is bubbling and golden brown on the top, approx. 30 minutes.