The Easy Chicken Pot Pie I Make on Weeknights

Name: The Easy Chicken Pot Pie I Make on Weeknights
Ingredients: 3 tablespoons olive oil; 4 medium carrots , diced; 4 celery stalks , diced; 1 medium yellow onion , finely diced; 1 1/2 teaspoons kosher salt , plus more to taste; 1 teaspoon freshly ground black pepper , plus more to taste; 1 cup fresh or frozen peas; 1 rotisserie chicken , meat picked and shredded into 1 to 2-inch pieces (about 4 cups ); 4 tablespoons unsalted butter; 1/4 cup ( 30 g ) all-purpose flour; 1 1/2 teaspoons dried dill; 1 teaspoon dried thyme; 1/2 teaspoon garlic powder; 1 1/2 cups chicken or vegetable broth; 1 1/2 cups plus 1 tablespoon whole milk , divided; 1 frozen puff pastry sheet