Prepare a baking pan by lining with parchment paper or Silpat. Prepare a pastry bag by fitting it with a ⅝-inch plain tip. Measure flour and set aside.
In a large saucepan, combine water, butter, salt, and chili powder. Bring to a boil over medium-high heat, stirring often.
Remove saucepan from heat. Add flour all at once. Stir until all the flour is moistened, about 1 minute.
Return to heat and cook, stirring constantly, for another 1 to 2 minutes until dough forms a smooth ball.
Transfer the dough to the bowl of an electric mixer and let cool for 5 minutes. Add eggs one at a time, beating well after each addition, until each egg is incorporated and dough is smooth. Mix in ½ cup gruyere and ¼ cup Parmesan cheese.
Fill prepared pastry bag with dough. Pipe dough into 2 inch round tall cone shapes.
Prepare the egg wash by whisking together the egg and 1 teaspoon water. Use a pastry brush to lightly coat the dough with egg wash and smooth out peaks and round the tops. Sprinkle remaining ¼ cup gruyere cheese on tops.
Bake for 5 minutes at 425°F. Reduce heat to 375°F and bake for an additional 30 minutes. Remove shells to a wire cooling rack to cool completely before filling.