Preheat the oven to 400°F. On a lightly floured surface, roll each pastry sheet into a 12x10-inch rectangle. Cut one sheet crosswise into six 2-inch strips. Cut the remaining sheet lengthwise into five 2-inch strips. On a baking sheet, closely weave the strips to make a 12x10-inch lattice. Place the lattice in the freezer while you prepare the filling. Editor’s Tip: Making the puff pastry lattice is similar to making a lattice pie crust or a bacon weave. If this is your first time, watch the video below to see each step in detail.

Toss the chicken with ½ teaspoon each salt and pepper. In a large skillet, heat 1 tablespoon butter over medium-high heat. Saute the chicken until browned, five to seven minutes. Remove the chicken from the pan, and set aside.

In the same skillet, heat the remaining butter over medium-high heat. Saute the onion until tender, five to seven minutes. Stir in the garlic, thyme and sage, and cook for one minute. Stir in the flour until blended. Cook and stir for one minute. Gradually stir in the broth and 1 cup half-and-half cream. Bring the mixture to a boil, stirring constantly. Cook and stir until thickened, about two minutes.

Stir in the frozen vegetables, lemon juice, chicken, and the remaining salt and pepper. Return the mixture to a boil.

Transfer the filling to a greased 2-½-quart oblong baking dish. Top it with the lattice, trimming the edges to fit. Editor’s Tip: Normally, you’d want to cut slits in the puff pastry to help the steam escape. Since you turned the pastry into a lattice, there’s no need!

Whisk together the egg yolk and the remaining cream. Brush it over the pastry. Editor’s Tip: An egg wash helps seal the puff pastry. It also gives the crust a glossy finish and golden-brown sheen.

Bake, uncovered, until the filling is bubbly and the pastry is golden brown, 45 to 55 minutes. Cover loosely with foil if the pastry starts getting too dark. Let the potpie stand for 15 minutes before serving.