unsalted butter, cut up
shredded gruyere cheese
finely chopped fresh rosemary
fresh ground black pepper
- Position a rack in the center of the oven.
- Line a large baking sheet with parchment paper or a silicone baking mat.
- Bring the milk and butter to a simmer in a heavy-bottomed medium saucepan over medium heat, stirring constantly to be sure the butter is completely melted by the time the milk simmers.
- Add the flour, all at once, and stir with a wooden spoon to make a thick paste.
- Decrease heat to low.
- Stir constantly until the paste comes together into a ball and films the bottom of the saucepan, about 1 minute.
- Adjust the heat as necessary so the paste cooks without burning.
- The idea here is to force off excess moisture, in the form of steam, from the paste in order to make a crisper pastry; remove the saucepan from the heat.
- Whisk 4 of the eggs in a bowl to combine them.
- One-fourth at a time, stir the beaten eggs into the hot dough in the saucepan, and stir well until the dough comes together into a glossy mass.
- Stir in the Gruyere, rosemary, mustard, salt, and pepper.
- Transfer the warm dough to a pastry bag fitted with a 1/2-inch plain tip.
- Pipe 25 walnut-size balls of dough, about 1 inch apart, onto the baking sheet.
- Or drop the dough from a teaspoon onto the sheet.
- Beat the remaining egg well with a pinch of salt.
- Lightly brush some of the egg glaze on the mounds of dough, being sure that the egg does no drip down onto the sheet.
- Bake until the balls are puffed and golden brown, 20-25 minutes.
- If the gougeres have not baked long enough, they will deflate when taken from the oven, so bake for at least 20 minutes before checking them.
- Remove the sheet from the oven.
- Pierce each gougere with the tip of a small knife (this releases the steam from the interiors of the puffs and helps crisp them).
- Return to the oven and continue baking until the gougeres are crisp, 5-8 minutes.
- Let cool briefly on the baking sheet.