Bring a large pot of salted water to a boil. Cook 9 ounces egg noodles according to package directions. Drain and set aside.
In a large skillet or Dutch oven, melt 2 tablespoons butter over medium heat.
Add 1 medium diced onion, 1 diced celery rib, and 2 peeled and diced carrots. Cook 3 minutes, stirring occasionally, until the vegetables begin to soften.
Add 1/2 teaspoon garlic powder, 1/2 teaspoon poultry seasoning, 1/2 teaspoon salt, 1/2 teaspoon pepper, and 2 tablespoons all-purpose flour. Stir to coat the vegetables and cook 1 minute to remove the raw flour taste.
Gradually whisk in 2 cups chicken broth until the mixture is smooth. Then whisk in 2 cups heavy cream.
Bring the sauce to a simmer. Add 2/3 cup frozen peas and 2/3 cup frozen corn and simmer 4 to 5 minutes, stirring occasionally, until the sauce has thickened.
Stir in 2 1/2 to 3 cups shredded cooked chicken and 1/3 cup shredded Parmesan cheese. Heat just until the chicken is warmed through and the cheese is melted.
Add the cooked noodles to the skillet and stir gently to combine and coat the noodles with the sauce.
Taste and adjust seasoning with additional salt and pepper if needed. Serve warm.