1 medium cauliflower, cut into florets
1 onion, very thickly sliced
½ small bunch flatleaf parsley, leaves picked and roughly chopped
½ tsp English mustard
40g/1½oz plain flour
sea salt and freshly ground black pepper
¼ tsp freshly grated nutmeg
40g/1½oz butter
40g/1½oz light mature cheddar, grated
600ml/1 pint semi-skimmed milk