Use a very good, strong cheese. If you like, one that’s aged adds a particularly nice flavor. I used Gruyère but other choices could be Comté, Emmenthal, Jarlsberg, Gouda (perhaps mixing smoked with regular), or even sharp cheddar. Any blue cheese will work here, too. Like the other cheese, the stronger, the better. The cayenne can be replaced by a few turns of freshly ground black pepper.
Serving and storage: Gougères are best freshly made, served warm, although they can be kept at room temperature for about a day. You can freeze them in an airtight bag for up to two months, reheating them in a medium-hot oven, until crisp.