Preheat the oven to 450˚ (230˚c ; fan-forced) and line a roasting tray with baking paper.
In a large bowl, toss the cauliflower florets, olive oil, salt, and pepper.
Arrange the cauliflower florets on the prepared roasting tray. Roast for 15-20 minutes, until golden and crisp.
In a small saucepan over low heat, heat the cheddar cheese, heavy cream, milk and butter. Stir often until smooth, being careful not to over-heat.
Once the cauliflower has roasted, transfer to a large bowl and pour the cheese sauce over. Gently fold the sauce into the cauliflower until coated evenly.