12 oz. water
6 oz. butter
salt, as needed
6.75 oz. flour, sifted
1.5 oz. egg whites
4.5 oz gruyere (or other) cheese
1.5 TB grated parmesan
Combine water, butter, and salt and bring to a boil. Add flour all at once and stir in well; cook over medium heat, stirring constantly until the dough stops sticking to the sides of the pot. Transfer to the mixer and mix on medium speed for about a minute. Add the egg white and eggs one at a time, mixing well after each addition to get a stiff but pliable texture. Add the cheeses and mix another minute. Transfer dough to a pastry bag with a plain round tip and pipe out onto parchment-papered cookie sheets. Bake at 400 degrees until golden brown, then turn down to 325 degrees and cook 12-15 more minutes.
Cheese puffs are best served warm, but you can also cool them and store them in an airtight container until ready to serve.
Choux pastry is pretty awesome stuff. It puffs like nothing else and you can make swans and other animals with it. Someday I would like to try doing eclairs with choux. There is a lot of room for creativity there- I imagine you could make some impressive pastries using different cake decorating tips.