Preheat your oven to 200°C (390°F). Spread the cauliflower florets on a baking sheet, drizzle with olive oil, and season with salt and pepper. Roast for 20-25 minutes, until edges are golden and fragrant, smelling nutty and slightly smoky.
While the cauliflower roasts, melt the butter in a saucepan over medium heat. Add the flour and whisk continuously for about 1 minute, creating a bubbly, golden roux.
Gradually pour in the milk while whisking vigorously to keep the mixture smooth. Bring to a gentle simmer and cook for 3-4 minutes until the sauce thickens and becomes silky.
Stir in the grated cheddar cheese until melted and smooth. Add a pinch of nutmeg, a squeeze of lemon juice, and season with salt and pepper to taste. Keep the sauce warm while you prepare the cauliflower.
Once the cauliflower is roasted and fragrant, transfer it into a large baking dish. Pour the cheese sauce evenly over the cauliflower, ensuring each piece is coated generously.
Sprinkle the breadcrumbs over the top for a crunchy finish. You can also add a little extra grated cheese if you like a cheesier top.
Bake uncovered for 15-20 minutes at 200°C (390°F), until the top is bubbling, golden, and crispy. The aroma of cheesy, toasted breadcrumbs will fill your kitchen.
Remove from oven and let rest for 5 minutes. This helps the sauce set slightly and makes serving easier. Serve hot, perhaps with a simple green salad for extra freshness.