Cook the bacon until crisp, drain it thoroughly, cool, and chop it finely. Line baking sheets with parchment paper and preheat the oven to 400°F (200°C).

Place the water, butter, and salt in a saucepan over medium heat. Bring the mixture to a full simmer so the butter melts completely.

Add the flour all at once and stir vigorously with a wooden spoon for 1–2 minutes, until the dough forms a smooth ball and pulls away from the pan. Continue stirring over low heat for another minute to dry the dough slightly.

Transfer the dough to a mixing bowl and let it cool for 5 minutes. Beat in the eggs one at a time, making sure the dough becomes smooth after each addition before adding the next egg.

Stir in the finely grated Parmesan, black pepper, and chopped bacon. Add the cayenne pepper or fresh chives if desired.

Pipe or spoon walnut-sized mounds, about 1 tablespoon each, onto the prepared baking sheets. Leave roughly 1 1/2 inches (4 cm) between mounds and sprinkle each with a little additional Parmesan.

Bake at 400°F for 10 minutes, then reduce the oven temperature to 375°F (190°C) and continue baking for 15–20 minutes. Do not open the oven during the first 15–20 minutes; the gougères are ready when deeply golden, puffed, and dry-looking.

Serve the gougères warm. For crisper puffs, turn off the oven, leave the door slightly open, and let them sit inside for 5 minutes before serving.