- 1 cup milk
- 4 tablespoons unsalted butter
- 1/2 teaspoon salt
- 1/4 teaspoon cayenne pepper
- 1 cup all-purpose flour
- 4 large eggs, at room temperature
- 1 1/2 cups grated Gruyere (about 6 ounces)
- Ham Mousse 
- Preheat the oven to 350 degrees F.
- Bring the milk, butter, salt and cayenne to a boil in a small saucepan. Remove from the heat.
- Place the flour in a large bowl. Add the hot liquid and stir well with a heavy wooden spoon until it comes together and forms a ball. Add the eggs 1 at a time, stirring well after the addition of each. Stir until the dough is satiny. Stir in the cheese and mix until dough is thick and cheese has mostly melted. Transfer to a pastry bag fitted with a medium plain tip.
- Pipe the dough in small mounds onto the prepared sheets. Bake until golden brown and puffed about 3 times their original size, 20 to 25 minutes. (Do NOT open the oven door for the first 10 to 15 minutes to keep them from deflating.)
- Remove from the oven and let cool slightly.
- With a paring knife, cut the top from each gougere, leaving either attached slightly (like a hinge), or remove. Pipe about 1 1/2 teaspoons of the mousse into the center of each gougeres and replace the tops.
- Arrange the mousse-filled gougeres on a platter, garnish with cornichons and chervil and serve.