Place a large pan of water onto boil and cover
Put the pasta in the boiling water
Melt the butter over a low heat in a medium sized pan
Add the flour to the butter and stir to combine, leave to cook for 2 mins stirring occasionally
Gradually add the milk, whisking to remove all lumps- this will take about 10 minutes
Once the milk is all mixed in, add in the grated cheese, Worcestershire sauce, mustard powder, pepper and nutmeg
Add the cheese sauce to the pasta and stir well
Serve