1) Heat oven to 180 to 190 degrees C/Gas 4 or 5.
2) Melt 90g of butter in a large saucepan over medium heat. Add flour and cook, stirring, for 1 minute. Whisk in the warmed milk and bring to a boil, continue to whisk constantly. The mixture will thicken as the heat increases. Continue to stir while adding the dry mustard, nutmeg, cayenne, salt, pepper, hot sauce and Worcestershire. Stir in the cheddar until it melts.
3) Pour the cheese sauce over the pasta and add to a 3 litre casserole dish.
4) Sprinkle the crisps, streaky bacon and parmesan on top and bake for 35 minutes.
5) Serve warm.