1 large cauliflower (about 1.3–1.4kg), cut into small florets

4 spring onions, white and green parts separated and sliced

70g butter

1 onion, roughly chopped

70g plain flour

1 tsp English mustard powder

750ml milk

150ml vegetable stock

150g mature cheddar, grated, plus 2 tbsp extra for topping

25g Parmesan, finely grated

4 tbsp single cream

2 tbsp fresh flatleaf parsley, finely chopped, plus extra to garnish (optional)

¼ tsp ground white pepper

Salt and freshly ground black pepper

For the topping:
900g potatoes, peeled or well scrubbed

1 tbsp vegetable oil

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Bring a large saucepan of water to boil. Add cauliflower, cover, and cook for 2 minutes after boiling. Drain and steam dry.
In another pan, gently cook white parts of spring onions, butter, and chopped onion until soft but not coloured.
Stir in flour and mustard powder. Gradually add milk and stock, stirring until thickened.
Remove from heat, stir in cheddar and Parmesan until melted. Add cream, parsley, white pepper, and salt.
Mix sauce with cauliflower in a large baking dish, then stir through green parts of spring onions.
Boil potatoes whole for about 15 minutes until almost cooked. Once cooled, slice into 5mm rounds and layer over cauliflower mixture.
Preheat oven to 200°C/180°C fan/Gas 6. Brush potato topping with oil, season, and bake for 30–40 minutes until golden and bubbling.
Finish under grill with extra cheddar until browned and cheesy. Garnish with parsley and serve.

Swap mature cheddar for Stilton, Gruyère, or Red Leicester for different flavors.
Add steamed broccoli, leeks, or spinach to the cauliflower mix for extra vegetables.
Sprinkle breadcrumbs over topping for added crunch.
Sweet potatoes can be used instead of regular potatoes, sliced thinner.