1/2 c butter (1 stick)
1 c water
1 c flour
1 c grated gruyere
1/2 c grated parmesan
2 t dijon mustard
fresh black pepper
Preheat oven to 425.
Heat butter and water in a medium saucepan over medium heat until butter is melted and mixture comes to a simmer.
Turn heat to low, add flour and stir until mixture starts to pull away from the sides of the pan (about a minute).
Remove pan from heat and add the eggs, one at a time, stirring well after each (dough will separate at first, but keep stirring and it will form a smooth paste).
Stir in remaining ingredients.
Drop mixture in heaping tablespoonfuls onto 2 greased or parchment-lined baking sheets. (At this point you can freeze them until you’re ready to bake).
Bake until puffed and brown, about 30 minutes. Cut slits in sides of puffs, return to oven and lower the heat to 350. Bake 10 minutes more.