Gruyere is difficult to come by where I live, can you suggest a substitute for Nigella's Croque Monsieur Bake?
Nigella's Croque Monsieur Bale (from NIGELLA EXPRESS) is a baked version of the ham and cheese sandwich and makes a perfect brunch or supper dish. The recipe includes Gruyere cheese as it melts well and has a good flavour. If you can't find Gruyere then Emmenthal would be a good substitute.
However if neither of these cheeses are available in your area then we suggest using a combination of half mature (sharp) cheddar and half firm mozzarella, to give stretchy, stringly melting cheese with a good flavour. For the mozzarella it should be the dry type that you use for pizza and not the soft, fresh type that is sold in balls. If you are in the US then you could also use Monterey Jack instead of the mozzarella.