This is one of those dishes that considering the simplicity of the ingredients, delivers more than you expect.
300ml of double cream
300ml of milk
6 anchovy fillets
100g of grated parmesan
100g of freshly grated breadcrumbs
salt & pepper
Firstly peel the onions and cut in half, I have tried this both cutting across and down the middle, it makes no difference. Place the onions cut side up in an ovenproof container, I use an enamel dish measuring 28 by 22 centimeters or a tarte tatin dish. mix the cream and milk and add the seasoning, pour into the dish so that the liquid comes roughly up to level of the onions.
Cut the anchovie fillets up into little pieces and place on top of each onion, finally sprinkle with the breadcrumbs and grated cheese, it's fine for this topping to fall in between the onions as well at this point, it will all cook into the cream and form a thick sauce.
Note: Its perfectly possible to make this without the anchovy for vegetarian friends, using vegetarian cheese, but the flavour of the anchovy enhances the dish without producing a pronounced anchovy flavour.