1 cup water
1 stick unsalted butter, cut up (1/2 cup butter = 1 stick)
1/2 teaspoon salt
1 cup all-purpose flour
4 large eggs
1 cup grated Gruyere cheese (4 oz)
black sesame seeds (for eyes)
Preheat oven to 400°F. Line two large baking sheets with parchment paper.
In a heavy saucepan bring water, butter, and salt to a boil, stirring to help melt butter. Add flour all at once and beat vigorously with a wooden spoon until mixture forms a dough. Continue beating over medium-low heat until dough is smooth and pulls away from sides and bottom of pan, about 2 minutes.
Remove pan from heat and let cool 2 minutes. Beat in eggs one at a time with the wooden spoon or an electric mixer, beating after each addition until batter is smooth again. Beat in the grated cheese.
Transfer dough to a pastry bag fitted with a 1/2-inch plain tube. Pipe “ghosts” onto lined baking sheet so that they are about 1-inch wide at base and 3 inches long, tapering to a point at top (they will be about 1/2-inch thick).
Press two black sesame seed eyes onto each ghost and bake in upper and lower thirds of oven, switching positions halfway through, until golden and crisp, about 25 minutes.