1 Cup Water
½ Cup Unsalted Butter
½ Teaspoon White Sugar
1 Cup All-Purpose Flour
1 Cup Grated Gruyere Cheese
⅛ Teaspoon Cayenne Pepper
⅛ Teaspoon Ground Black Pepper
4 Tablespoons Grated Gruyere Cheese
3 Eggs, Or More As Needed
Step 1 Preheat the oven to 425 degrees F (220 degrees C). Line a baking sheet with parchment paper.
Step 2 Combine water, butter, and sugar in a saucepan and bring to a boil. Remove from heat and immediately add flour. Stir quickly with a wooden spoon for 30 seconds to 1 minute.
Step 3 Return pan to heat and stir to let excess moisture evaporate, 30 seconds to 1 minute. Scoop dough into the bowl of a stand mixer fitted with a paddle attachment. Let cool slightly.
Step 4 Add 3/4 cup Gruyere cheese, cayenne, and black pepper to the dough. Beat in eggs, 1 at a time, scraping down the bowl after each addition. If mixture still clings to the beaters, add a fourth egg.
Step 5 Pipe or spoon tablespoonfuls of dough 2 inches apart onto a the prepared baking sheet. Add a small pinch of remaining Gruyere cheese on top of each puff.
Step 6 Bake in the preheated oven for 10 minutes. Lower temperature to 375 degrees F (190 degrees C), and bake until puffed and golden brown, about 15 minutes more.