For the base:
1) Cook pasta until al dente in a large pot of boiling salted water. Drain.
2) Meanwhile, in a large saucepan, melt the butter over medium heat. Add the flour and stir to form a smooth paste. Cook for about 2 minutes, being careful not to brown.
3) Gradually add the milk and the single cream and simmer until thickened slightly, stirring all the while. Remove from the heat.
4) Stir in the 3 cheeses and season with black pepper, to taste. Add the cooked pasta and mix into the cheese sauce thoroughly.
6) Preheat oven to 200 degrees C/Gas 6.
For the classic mac and cheese:
1) Pour half of the mac and cheese into an 20 by 20 by 5cm baking dish.
2) In a mixing bowl toss the bread crumbs together with the melted butter, parsley, and salt, to taste. Top the mac and cheese with the bread crumb mixture and bake 15 minutes or until the topping has nicely browned and pasta is bubbly and creamy.
For the chilli mac and cheese:
1) Stir the chilli powder and chilli flakes into half of the mac and cheese base. Pour into an 20 by 20 by 5cm baking dish.
2) In a mixing bowl combine the crushed corn crisps together with the oil and the lime zest. Top the mac and cheese with the corn crisp mixture and bake 15 minutes or until the topping has nicely browned and pasta is bubbly and creamy.