Chicken Pot Pie (The Best)

Name: Chicken Pot Pie (The Best)
Prep time: 25 min
Cook time: 1 h 5 min
Total time: 1 h 30 min
Cuisine: American
Ingredients: 6 tbsp (80 g) unsalted butter, softened; ¼ cup (40 g) unbleached all-purpose flour; 1 tbsp cornstarch; 1/2 cup (125 ml) milk; 1 small onion, finely chopped; 1 carrot, peeled and diced; 1 celery stalk, diced; 1 can (10 oz/284 ml) condensed chicken broth; ½ cup (80 g) russet potato, peeled and diced; 1 ½ cups (255 g) cooked chicken, diced (1/2 store-bought roasted chicken, approximately); ½ cup (75 g) frozen peas; 2 cups (300 g) unbleached all-purpose flour; 1/2 tsp salt; 1 cup (225 g) cold unsalted butter, cut into cubes; 1/4 cup (60 ml) ice water; 1 tbsp (15 ml) white vinegar; Milk, for brushing