Cook the macaroni in plenty of boiling salted water for about 12 minutes then drain.
Meanwhile fry the onion, garlic and carrots until soft and lightly coloured. Add the mince and continue stirring for 5 minutes until the mince has browned.
Add the stock, bay leaf, Worcestershire sauce and seasonings; cover and simmer for 15-20 minutes. Discard the bay leaf. Taste and adjust the seasonings and stir in the oregano.
To make the sauce melt the butter in a saucepan and stir in the flour. If not smooth enough add a little more butter.
Gradually add the milk and bring to the boil, stirring continuously. Simmer for 3 minutes, season to taste and stir in one-third of the grated cheese until melted.
In a lightly greased ovenproof dish layer up one-third of the cooked macaroni followed by half the meat and half the sauce. Continue with half the macaroni, remaining meat, remaining macaroni and finally the sauce.
Sprinkle with the remaining cheese and cook in a moderately hot oven of 200 degrees C for about 40 minutes until well browned.
Leave it to rest for 15 minutes, this helps keep it together when dishing it out then put back in the oven for 5 minutes to heat, then serve