- For filling:
- 1 small tomato
- 1 small onion, finely chopped
- 2 tablespoons unsalted butter
- 1/8 teaspoon salt
- 2 large white mushrooms, finely chopped
- 1 tablespoon all-purpose flour
- 6 tablespoons reduced-sodium chicken broth
- 1 1/4 cups finely chopped cooked turkey
- 1 tablespoon chopped fresh flat-leaf parsley
- For cream puff:
- 3/4 cup water
- 6 tablespoons cold unsalted butter, cut into small pieces
- 1/2 teaspoon salt
- 3/4 cup all-purpose flour, sifted after measuring
- 4 large eggs, at room temperature for 30 minutes
- 3 ounces Swiss cheese, cut into 1/4-inch dice
- 2 tablespoons finely grated Parmigiano-Reggiano (using a Microplane rasp)
- 1/2 teaspoon dry mustard powder
- Make filling: Using a sharp knife, cut a shallow X in bottom of tomato and immerse in a saucepan of boiling water 10 seconds. Immediately transfer tomato with a slotted spoon to a bowl of ice and cold water to cool, then drain. Peel, seed, and finely chop tomato.
- Cook onion in butter with salt in a 10-inch heavy skillet over moderate heat, stirring occasionally, until golden, about 4 minutes. Add mushrooms and cook, stirring occasionally, until mushrooms begin to brown, about 3 minutes. Sprinkle with flour and cook, stirring constantly, 1 minute, then stir in broth and bring to a boil over moderate heat, stirring constantly. Reduce heat and simmer, stirring, 1 minute (sauce will be thick). Remove from heat and stir in turkey, parsley, chopped tomato, and pepper to taste.
- Make Cream Puff Dough: Put oven rack in middle position and preheat oven to 375 degrees F.
- Bring water to a boil with butter and salt in a 1 1/2- to 2-quart heavy saucepan. Reduce heat to low and add flour all at once, then stir vigorously with a wooden spoon until dough forms a ball and pulls away from sides of pan, 1 to 2 minutes.
- Remove from heat and stir vigorously for 1 minute more to release steam, then beat in 3 eggs, 1 at a time, beating until incorporated after each addition. Stir in Swiss cheese, 1 tablespoon parmesan, and mustard, then spread dough with dampened hands into a buttered 9-inch pie plate. Create a 6-inch-wide hole in center by pulling dough toward edge of pie plate, then mound filling in hole. Push dough 1 inch up sides of filling, leaving top of filling exposed. Lightly beat remaining egg and brush some over dough (reserve remainder for another use), then sprinkle with remaining tablespoon parmesan.
- Bake pie until dough is puffed and golden, about 40 minutes, then cut 4 slits with a small knife around side of dough to release steam and bake 10 minutes more. Let pie stand 5 minutes before serving.