Preheat Your Oven: First things first, preheat your oven to 180°C (160°C fan/Gas Mark 4). Lightly butter a medium-sized baking dish (around 20x30cm).

Prepare the Cauliflower: Bring a large pan of salted water to the boil. Add the cauliflower florets and cook for 4-5 minutes until they are just tender-crisp. You don't want them soft. Drain them thoroughly and let them steam-dry in the colander for a few minutes to get rid of excess water. This step is crucial for a thick sauce.

Start the Béchamel Sauce: While the cauliflower drains, melt the 50g of butter in a medium saucepan over a medium heat. Once melted, stir in the flour to form a paste, known as a roux. Cook this for about 1-2 minutes, stirring constantly, until it smells slightly nutty.

Build the Sauce: Gradually pour the warm milk into the roux, a little at a time, whisking continuously to prevent lumps. What works best for me is adding about 100ml at first and whisking it into a thick, smooth paste before adding the rest of the milk in a slow, steady stream. For more tips, BBC Good Food has a great guide on how to make a perfect béchamel sauce.

Simmer and Thicken: Bring the sauce to a gentle simmer and cook for 5-7 minutes, stirring often, until it has thickened enough to coat the back of a spoon.

Add the Flavour: Remove the pan from the heat. Stir in the Dijon mustard, grated nutmeg, and most of the grated cheddar and Gruyère (reserving a small handful of each for the top). Stir until the cheese is completely melted and the sauce is smooth. Season generously with salt and pepper.

Assemble the Bake: Arrange the drained cauliflower florets in your prepared baking dish. Pour the cheese sauce evenly over the top, making sure to get it into all the gaps.

Prepare the Topping: In a small bowl, mix together the breadcrumbs, grated Parmesan, chopped parsley, and the reserved cheddar and Gruyère. Drizzle with the olive oil and toss to combine.

Bake to Perfection: Sprinkle the breadcrumb mixture evenly over the cauliflower cheese. Bake for 25-30 minutes, or until the top is golden brown and the sauce is bubbling deliciously around the edges.

Rest and Serve: Let the bake rest for 5-10 minutes before serving. This allows the sauce to set slightly, making it easier to serve.