Don't let the fancy French name for these cheese puffs mislead you--this is an easy appetizer recipe. They're traditionally made with Gruyère or Comté; we couldn't resist turning to our Vermont roots and using good old Cheddar instead.
Position racks in upper and lower thirds of oven; preheat to 400 degrees F. Line 2 large baking sheets with parchment paper.
Combine water, butter and salt in a medium saucepan. Bring to a simmer over medium-high heat. Reduce heat to medium-low, add flour and mix vigorously with a wooden spoon to form a smooth dough. Cook, stirring, for 2 minutes. The dough should dry out slightly and pull away from the pan.
Scrape the dough into a medium bowl and let cool for 2 minutes. Using a wooden spoon, beat eggs one at a time into the dough, beating thoroughly after each addition. The batter will separate after each egg, but keep stirring: it will come back together. Add cheese, mustard, thyme and rosemary and fold to combine.
Transfer the dough to a pastry bag fitted with a round 3/8- to 3/4-inch pastry tip (or use a gallon-size plastic bag with about 3/4 inch snipped off a corner). Pipe 25 small mounds of dough onto each prepared baking sheet, making each a littler wider than a quarter.
Bake, rotating the pans front to back and top to bottom halfway through, until puffed and golden, 18 to 20 minutes. Serve warm.
To make ahead: Freeze cooled gougères airtight for up to 2 weeks. Reheat for 12 to 15 minutes at 350 degrees F.
Equipment: Pastry bag with a medium (3/8- to 3/4-inch) round tip (or gallon-size plastic bag), parchment paper