Preheat your oven to 220°C (425°F).

Remove the outer leaves from the cauliflower.

Set aside the leaves.

Remove the florets from the main stalk and cut them into evenly sized, fairly chunky pieces. Place the florets onto a baking tray.

Cut the leaves away from the main stalk. Wash them thoroughly, pat them dry, and cut them into slightly smaller pieces.

Drizzle the cauliflower florets (and leaves) with olive oil and season generously with salt and black pepper.

Place the tray into the preheated oven and roast for 25–30 minutes, or until the cauliflower begins to lightly brown.

While the cauliflower is roasting, place a saucepan over a medium-low heat. Add the butter and allow it to melt.

Add the flour to the melted butter and stir to form a roux. Cook until it turns golden brown.

Stir in the Dijon mustard until fully incorporated.

Gradually add the milk and cream mixture a splash at a time, whisking continuously until smooth.

Simmer the sauce gently for 5–10 minutes, stirring regularly, until it thickens.

Whisk in the grated mature cheddar cheese until fully melted and smooth.

Taste the sauce and season with salt and black pepper as needed.

Remove the cauliflower from the oven once roasted.

Transfer all of the roasted cauliflower and leaves to a roasting or baking dish. Pour the cheese sauce evenly over the top.

Optionally, sprinkle over the additional 50g of cheddar.

Reduce the oven temperature to 200°C (390°F) and bake for 25–30 minutes, or until golden and bubbling on top.

Allow it to cool for 5–10 minutes before serving.

Serve warm as a side dish or main.