Preheat your oven to 200°C (180°C fan) and bring a large pot of salted water to a vigorous, rolling boil. You will know the water is ready when the surface looks like a stormy sea, with large bubbles breaking quickly. Add the macaroni and cook for 2 minutes less than the package instructions suggest — the pasta should be firm to the bite, with a tiny white dot in the centre when you cut a piece in half. Drain it in a colander and set it aside.

While the pasta cooks, start the cheese sauce. In a large saucepan, melt the butter over a medium heat. Once it has completely turned to liquid and begins to foam gently, whisk in the plain flour. Cook this mixture, stirring constantly, for about 1 minute until it smells slightly nutty and turns a pale, biscuit colour — this is your roux.

Slowly pour in the warm milk, whisking continuously. The mixture will seize up into a thick paste at first, but keep whisking. After about 2 minutes, the sauce will loosen and begin to steam, thickening to the consistency of double cream. You will see it coating the back of a wooden spoon, leaving a clean trail when you run your finger through it.

Remove the pan from the heat and stir in the mustard powder, garlic powder, and a generous pinch of salt and pepper. Add the grated cheddar and Gruyère in three batches, stirring gently after each addition until the cheese has completely melted and the sauce is a glossy, pale yellow. The smell at this stage should be deeply savoury, with a tang from the cheese.

Fold the drained macaroni into the cheese sauce. Use a spatula to gently combine everything until every piece of pasta is coated. The sauce will look thick and clingy, wrapping around the macaroni rather than pooling at the bottom of the pan. Taste a piece of pasta and adjust the seasoning if needed.

Transfer the mixture to a buttered baking dish (or four individual ramekins for a more polished presentation). In a small bowl, mix the breadcrumbs, grated Parmesan, and olive oil together until the crumbs look like damp sand. Sprinkle this topping evenly over the mac and cheese, covering the surface completely.

Bake for 15-18 minutes, or until the topping is golden brown and the sauce is bubbling around the edges. You will hear a gentle sizzle as it bakes, and the kitchen will fill with the aroma of toasted bread and melted cheese. For an extra touch, switch the oven to the grill setting for the final 2 minutes to achieve a deeper, nutty brown colour on the crumb topping. Let it rest for 5 minutes before serving, then garnish with fresh parsley.