Preheat oven to 220°C / 430°F (200°C fan).

Toss cauliflower in oil, salt and pepper. Spread on a large tray.

Roast 20 minutes (don't turn). Cauliflower should still be a bit firm, but with some colour on them. Remove from oven.

Turn oven down to 180°C/350°F.

Heat milk: Heat milk and cream until hot – either on the stove or in microwave.

Make roux: Melt butter in a large saucepan or small pot over medium heat. Add flour and cook, stirring regularly, for 3 minutes.

Add milk: While stirring, pour in half the milk. Once the roux is dissolved into the milk (mixture will thicken), stir in remaining milk. Stir on the heat for 1 minute – mixture should be thick enough to coat a wooden spoon.

Add cheese: Turn the stove off, but leave the pot on the turned off stove. Stir in salt, nutmeg and both cheeses. The cheese will thicken the mixture so it's like a thick sauce.

Mix in cauliflower: Add cauliflower and toss to coat in the sauce.

Fill baking dish: Transfer mixture to a 2L / 2qt baking dish (30 x 20 x 5cm / 12 x 8 x 2").

Top with cheese: Sprinkle over gruyère followed Red Leicester cheese.

Bake at 180°C/350°F for 30 minutes until the cheese is melted, and cauliflower is bubbly and golden.

Serve: Sprinkle with parsley if desired. Stand 5 minutes then serve!