Preheat your oven to 220°C. Toss the cauliflower florets in olive oil, salt, and pepper. Roast for 20 minutes.
While that’s in the oven, melt your butter in a pan. Whisk in the flour until it forms a smooth paste.
Gradually pour in the milk, whisking constantly to get rid of any lumps. Add garlic powder, onion flakes, nutmeg, thyme, and a pinch of salt and pepper.
Once the sauce starts bubbling, turn off the heat and stir in the cheese until melted and smooth.
Pour the sauce over your roasted cauliflower, then top with a mixture of panko crumbs, Parmesan, and melted butter.
Pop the dish back in the oven at 180°C for 15 minutes until the top is golden and crispy.