1 medium cauliflower (around 700g/1lb 9oz), cut into florets, stem sliced and green outer leaves thickly shredded
1 tsp English or Dijon mustard
flaked sea salt and ground black pepper
50驳/1戮辞锄 plain flour (or gluten-free plain flour)
50驳/1戮辞锄 butter
120g/4陆oz mature cheddar, coarsely grated
500ml/18fl oz milk