Cook the pasta according to the packet instructions, reducing the time by 1 minute.
Meanwhile, melt the butter in a saucepan over a medium heat. When foaming, Add the garlic clove and mustard and stir for 30 seconds. Add the flour and cook for a couple of minutes. This is a basic roux and cooking it out for a couple of minutes means the sauce will not taste of flour.
Pour the double cream and the milk into a jug. Gradually add the milk and cream into the roux continuing to stir until it is all incorporated. Bring to the boil, stirring constantly until thick and saucy. This can take five or so minutes.
Add a teaspoon of white pepper, around a quarter of the grated nutmeg and a good grinding of salt.
Grate the cheese into the sauce and stir to melt.
Fry the bacon until really crisp. Then heat the grill to high.
Drain the pasta, retaining around a cupful of the pasta water. Then stir the pasta into the sauce and add a few tablespoons of pasta water to loosen the sauce to the right consistency.
Put the macaroni cheese into a baking dish, grate some more cheese on top and grill until browned and bubbling.
Break up the bacon into little bits and stir through some parsley and freshly ground black pepper.
Top the Ultimate Mac & Cheese with the bacon and some black pepper and serve immediately whilst still bubbling!