1 package (17.3 ounces) frozen puff pastry, thawed
2 pounds boneless skinless chicken breasts, cut into 1-inch pieces
1 teaspoon salt, divided
1 teaspoon pepper, divided
4 tablespoons butter, divided
1 large onion, chopped
2 garlic cloves, minced
1 teaspoon minced fresh thyme or 1/4 teaspoon dried thyme
1 teaspoon minced fresh sage or 1/4 teaspoon rubbed sage
1/2 cup all-purpose flour
1-1/2 cups chicken broth
1 cup plus 1 tablespoon half-and-half cream, divided
2 cups frozen mixed vegetables (about 10 ounces)
1 tablespoon lemon juice
1 large egg yolk
1. Preheat oven to 400°. On a lightly floured surface, roll each pastry sheet into a 12x10-in. rectangle. Cut 1 sheet crosswise into six 2-in. strips; cut remaining sheet lengthwise into five 2-in. strips. On a baking sheet, closely weave strips to make a 12x10-in. lattice. Freeze while making filling.
2. Toss chicken with 1/2 teaspoon each salt and pepper. In a large skillet, heat 1 tablespoon butter over medium-high heat; saute chicken until browned, 5 to 7 minutes. Remove from pan.
3. In same skillet, heat remaining butter over medium-high heat; saute onion until tender, 5 to 7 minutes. Stir in garlic and herbs; cook 1 minute. Stir in flour until blended; cook and stir 1 minute. Gradually stir in broth and 1 cup cream. Bring to a boil, stirring constantly; cook and stir until thickened, about 2 minutes.
4. Stir in vegetables, lemon juice, chicken and the remaining salt and pepper; return to a boil. Transfer to a greased 2-1/2-qt. oblong baking dish. Top with lattice, trimming to fit.
5. Whisk together egg yolk and remaining cream; brush over pastry. Bake, uncovered, until filling is bubbly and pastry is golden brown, 45 to 55 minutes. Cover loosely with foil if pastry starts getting too dark. Let stand 15 minutes before serving.
TOTAL TIME: Prep: 45 min. Bake: 45 min. + standing
YIELD: 8 servings.