1. Preheat oven to 350 degrees. Line baking sheets with parchment paper; set aside.

2. In a large saucepan bring milk, 1 cup water, butter, and salt to a boil over medium-high heat. Add flour and espelette pepper; cook, stirring constantly, until dough pulls away from sides of pan, 5 to 10 minutes. Remove from heat and let cool slightly, about 5 minutes.

3. Add eggs, one at a time, stirring after each addition. Drop 3-tablespoon-size scoops of dough 2 inches apart on prepared baking sheets. Top each with 1 tablespoon Gruyere cheese; sprinkle with fleur de sel, cracked black pepper, and espelette pepper.

4. Transfer to oven and bake until puffy and browned, rotating pan halfway through baking, about 30 minutes. Serve warm or at room temperature.