Preheat the oven to 325 degrees F. Line a baking sheet with parchment paper.
In a saucepan, bring the milk, water, and butter to a boil. Remove from the heat and stir in the flour and salt. Place back on low heat and gently cook while stirring to dry out the mixture a little bit.
Place in a mixer with the paddle attachment. On low speed, incorporate the eggs one at a time. Finish with the Grana Padano, cayenne, truffle oil or salt, and chives.
Using a pastry bag fitted with an open tip, pipe to the size of a quarter and bake for about 12 minutes, until golden brown.