In large Dutch oven or soup pot, melt 4 tablespoons butter over medium heat. Add onion, celery, carrots, and mushrooms. Sauté 7 minutes until softened. Add garlic and stir 1 minute until fragrant.
Sprinkle flour over vegetables. Stir constantly for 2-3 minutes until vegetables are coated and raw flour smell disappears. Mixture will look pasty.
Slowly pour in chicken broth while stirring continuously to prevent lumps. Add cubed potatoes and bring to gentle simmer. Cook uncovered 12 minutes until potatoes are fork-tender.
Stir in shredded chicken, frozen peas, frozen corn, and heavy cream. Simmer 5 more minutes until everything is heated through.
Add chopped parsley, salt, and black pepper. Taste and adjust seasoning as needed.
Remove from heat and let soup sit covered for 10 minutes. This allows flavors to deepen and soup to thicken perfectly before serving.
Notes
Use rotisserie chicken to save time. You’ll need about 3 cups shredded.
Don’t rush the flour step. Cook until nutty aroma develops for best flavor.
Soup thickens as it sits. Add broth or cream when reheating if too thick.
For gluten-free version, substitute flour with gluten-free blend or cornstarch slurry.