Put milk, onion, peppercorns and bay leaf in a pan and bring to a boil. Remove from the hear and let stand for 15 mins.

Melt the butter in a pan and stir in the flour until well combined and smooth. Cook over med heat, stirring constantly, for 1 min. Remove from heat. Strain the milk and stir a little in the butter and flour mixture until well incorporated. Return to the heat and gradually add the remaining milk, stirring constantly until the sauce is smooth and thickened, then add the nutmeg, cream and pepper to taste. Add the cheddar and roquefort cheeses and stir until melted.

Meanwhile, bring a large pan of water to a boil. Add the macaroni, then return to a boil and cook for 8-10 mins, or until just tender. Drain well and add to the cheese sauce. Stir well together.

Preheat the boiler to high. Spoon the macaroni and cheese into an ovenproof serving dish, then scatter over the gruyere cheese and cook under the broiler until bubbling and brown.