Mac and Cheese with Mushrooms

2 tbsp extra virgin olive oil

salt and freshly ground black pepper

2 – 3 tbsp marjoram, chopped

225g (8oz) macaroni or ditalini

50g (2oz) butter

150g (5oz) onion, finely chopped

2 cloves garlic, crushed

50g (2oz plain flour

850ml (scant 1 1/2 pints) boiling whole milk

1/4 tsp Dijon or English mustard

1 tbsp chopped flat-leaf parsley (optional)

225g (8oz) freshly grated mature Cheddar cheese or a mix of Cheddar, Gruyère and Parmesan

25g (1oz) freshly grated Cheddar or Parmesan cheese, for sprinkling on top (optional)

sea salt and freshly ground black pepper