• 4 tablespoons unsalted butter
• 1⁄4 cup milk
• 1/2 cup water
• 1 1/2 teaspoons kosher salt, divided
• Pinch of white pepper
• 3⁄4 cup all-purpose flour
• 1/8 teaspoon baking powder
• 1 cup grated Gruyère
• 3 large eggs, at room temperature
• 2 tablespoons heavy cream
1. Preheat the oven to 400° F. Combine the butter, milk, water, 1/2 teaspoon salt and white pepper in a 2-quart saucepot, and bring to a boil over medium heat.
2. Sift together the flour and baking powder, and add all at once to the liquid. Remove from heat. Stir well with a wooden spoon, and return to the stove. Cook over medium heat, stirring constantly, until the dough pulls away from the side of the pot, a few minutes.
3. Remove from heat, and transfer the dough to the bowl of an electric mixer fitted with the paddle attachment. Add 3/4 cup Gruyère, and mix on low until just warm, about 2 minutes.
4. Increase the speed of the mixer to medium-high, and add the eggs one at a time. Continue to mix the dough until it is smooth and shiny, about 10 minutes. Let the mixture cool to room temperature.
5. Line two large baking sheets with parchment paper. Transfer the dough to a pastry bag fitted with a #6 tip (an opening about the size of a nickel). Pipe the dough into 1-inch rounds, each about 1/2-inch high. Each baking sheet should fit 25 to 28 gougères. Brush the gougères with the heavy cream. Sprinkle with the remaining 1/4 cup Gruyère and 1 teaspoon salt.
6. Place the baking sheets in the oven, and bake for 5 minutes. Turn the trays 180 degrees, and continue to bake until the gougères take on a deep golden-brown color, about 8 to 10 minutes more. Makes 50 to 55 gougères.
Do-Ahead Tip: You can make and refrigerate the dough up to three days in advance, or bake the gougères ahead of time. Cover the cooled puffs loosely with paper towels or leave them open to the air to retain maximum crispness, then reheat them in a 400° F oven for about two and a half minutes, right before serving.