1. Preheat oven to 200°C (Gas Mark 6).
2. Bring a large pan of water to the boil, then add the cauliflower and cook for 2 minutes.
3. Drain and place in an ovenproof dish.
4. Place the margarine into a saucepan and gently heat to melt it.
5. Mix in the flour, stirring for 1 to 2 minutes until the roux is lightly golden.
6. Remove from the heat and gradually whisk in the milk to form a smooth sauce.
7. Return to the heat and simmer for 2 to 3 minutes.
8. Remove from the heat and mix in the mustard and Worcestershire sauce.
9. Season with black pepper and flake the salmon into the sauce, stirring carefully.
10. Pour the sauce over the cauliflower and top with the grated cheese.
11. Place in the oven and cook for 10-15 minutes, until golden brown.
1 large cauliflower, cut into florets
40g (1½oz) margarine
40g (1½oz) plain flour
450ml (¾ pint) semi-skimmed milk
1 teaspoon English mustard
½ teaspoon Worcestershire sauce
Black pepper, to season
150g (5oz) salmon, flaked
120g (4½oz) mature cheddar cheese