Foryoueats: Chicken Pot Pie

Ingredients

• 1 to 2 packages frozen puff pastry, best quality such as Dufour or Pepperidge Farm, thawed (see note)
• 4 tablespoons unsalted butter
• 1 medium yellow onion, diced
• 3 cloves garlic, roughly chopped
• 3 stalks celery, diced
• 1 cup frozen pearl onions (no need to defrost)
• 3 carrots, sliced into ¼-inch rounds
• ⅓ cup all-purpose flour, plus more for rolling the pastry
• 2½ cups low-sodium chicken broth
• ⅓ cup Cognac or brandy (okay to replace with more chicken broth if avoiding alcohol)
• ¾ teaspoon salt
• ½ teaspoon white pepper
• ½ cup heavy cream
• 1 tablespoon chopped fresh thyme (or a combination thyme, rosemary and sage), plus a few thyme springs for serving
• 3-4 cups shredded cooked chicken, from 1 rotisserie chicken
• 1 cup frozen peas (no need to defrost)
• 1 egg