1/4 cup (1/2 stick) unsalted butter
1 large shallot, finely chopped
1 tablespoon chopped fresh thyme
1/3 cup Wondra or all-purpose flour, plus more for surface
3 cups low-sodium chicken broth
1 cup whole milk
Kosher salt and freshly ground black pepper
6 oz. carrots (about 6 small), peeled, chopped
4 cups coarsely chopped or shredded chicken meat (from 1 small rotisserie chicken)
1 1/2 cups frozen pearl onions, thawed
1 1/2 tcups frozen peas, thawed
1/4 cup chopped fresh flat-leaf parsley
1 sheet frozen puff pastry (one 14-oz. package or half of 17.3-oz. package), thawed in refrigerator
1 large egg, beaten to blend
Preheat oven to 400°. Heat butter in a large skillet over medium heat. Add shallot and thyme and cook, stirring often, until shallot is translucent and golden, about 4 minutes. Add ? cup flour and cook, whisking constantly, until mixture is pale golden and smells like popcorn, 5–8 minutes.
Whisk in broth ½-cupful at a time, incorporating completely before adding more. Whisk in milk; season with salt and pepper. Bring to a boil, reduce heat, and simmer, whisking occasionally, until mixture is thick enough to coat a spoon, 10–15 minutes. Add carrots and cook until just tender, about 5 minutes.
Mix in chicken, onions, peas, and parsley; season with hot sauce, Worcestershire sauce, salt, and pepper.
Transfer mixture to a shallow 2-qt. baking dish. Unfold pastry and gently roll out on a lightly floured work surface just to smooth creases and make large enough to fit over dish, if needed. Drape over baking dish and trim pastry so it is slightly larger than the dish (you want a little overhang). Brush with egg and make 2 or 3 slits in the pastry with a sharp knife.
Place baking dish on a rimmed baking sheet (to catch any filling that may drip over) and bake until puff pastry is golden brown and filling is bubbling through slits in pastry, 20–25 minutes. Reduce heat to 350° and bake until puff pastry is deep golden brown and cooked through, 30–35 minutes longer. Let sit 10 minutes before serving.
From Bon Appetit.