Cook the Pasta and Broccoli: Bring a large pot of generously salted water to a rolling boil. Add the macaroni and cook according to package directions, but for 2 minutes less than the recommended time. For the last 3 minutes of cooking, add the broccoli florets to the pot with the pasta. This blanches them perfectly so they're tender but not mushy.

Drain and Set Aside: Once cooked, drain the pasta and broccoli well and set them aside. You can use the same pot to make the sauce to save on washing up.

Start the Roux: Place the empty pot back on the hob over a medium heat. Add the butter and let it melt completely. Once it’s foaming, stir in the plain flour to form a thick paste. Cook this roux for 1-2 minutes, stirring constantly. This step is important to cook out the raw flour taste.

Make the Béchamel Sauce: Gradually add the milk to the roux, a little at a time, whisking vigorously after each addition to ensure there are no lumps. Once all the milk is incorporated, switch to a wooden spoon and let the sauce simmer gently for 5-7 minutes, stirring often, until it has thickened enough to coat the back of the spoon.

The Most Important Step: Turn the heat off completely. Let the sauce sit for a minute to cool slightly. I used to struggle with grainy cheese sauces until I discovered this simple trick of taking the pan off the heat. It makes all the difference.

Add the Flavour: Stir in the mustard powder and grated nutmeg. Season generously with salt and freshly ground black pepper. Now, add the grated cheddar and Gruyère cheese to the pot. Stir gently until all the cheese has melted and the sauce is smooth, glossy, and gloriously cheesy.

Combine Everything: Pour the cooked pasta and broccoli back into the pot with the cheese sauce. Stir everything together until the pasta and florets are completely coated.

Serve or Grill: You can serve the broccoli mac and cheese immediately as a creamy, stove-top version. Alternatively, for a golden, crunchy top, transfer it to an ovenproof dish. Mix the panko breadcrumbs and Parmesan cheese together and sprinkle evenly over the top. Place under a hot grill for 3-5 minutes, or until the top is golden brown and bubbling. Keep a close eye on it, as it can catch quickly!