Break cauliflower into florets, wash and cut stalks with a sharp knife. Place the florets in a large plate, sprinkle with salt and pour over some water.
Cover with cling wrap and microwave on High for 8 - 10 minutes (depending on the size of the cauliflower). Drain off excess liquid and reserve for sauce.
Return cling wrap covering over cauliflower and allow to stand while making sauce.
Place the butter in a microwave proof mixing bowl and cook on High for 40 seconds to melt it.
Add flour, salt and pepper, stir well and cook for a further 30 seconds on High.
Gradually stir in milk and cook on High for 2 minutes. Stir around the edges of the bowl and return to oven for a further 2.5 minutes on High. (Caution: It is very important to slowly add milk while stirring continuously to prevent lumps forming).
Beat sauce well and pour over cauliflower. Sprinkle with a mixture of cheese and breadcrumbs. Return to oven for 2 minutes on High to melt cheese and reheat cauliflower. If desired, place cauliflower under a conventional griller to make it crisp and brown instead of cooking for the last two minutes.