Mom's Fabulous Chicken Pot Pie with Biscuit Crust

Ingredients (16)

• + ¼ cup butter add to pantry
• ✓ 1 small onion, chopped
• + 3 celery ribs, chopped add to pantry
• + 3 carrots, chopped add to pantry
• + ⅔ cup frozen peas add to pantry
• ✓ 3 tablespoons chopped fresh parsley
• + ¼ teaspoon dried thyme add to pantry
• + ¼ cup all-purpose flour add to pantry
• + 2 cups lower-sodium chicken broth add to pantry
• + ⅔ cup half-and-half cream add to pantry
• ✓ salt and ground black pepper to taste
• + salt and ground black pepper to taste add to pantry
• + 3 cups cooked chicken, cut into bite-size pieces add to pantry
• + 1 (16.3 ounce) can refrigerated flaky-style biscuits (such as Pillsbury Grands®) add to pantry
• + 1 egg yolk, beaten add to pantry
• + 1 tablespoon water add to pantry