Heat a dutch oven or soup pot over medium/high heat and melt in 6 Tbsp butter. Add chopped onion, chopped celery, and sliced carrots and sauté 5-7 minutes, stirring occasionally, until softened and lightly golden.
Add sliced mushrooms and garlic and sauté for another 5 minutes, stirring occasionally until softened.
Add ⅓ cup flour and stir constantly for 1 minute until golden.
Add 6 cups chicken stock, sliced potatoes, 3 ½ tsp salt (or to taste), and ½ tsp black pepper. Bring to a boil then reduce heat to a simmer, partially cover and cook 12-15 minutes or just until potatoes are tender.
Add shredded chicken, frozen peas, and frozen corn, ½ cup heavy whipping cream and ¼ cup parsley. Bring back to a simmer and continue to cook for another 5 minutes or until peas and corn are tender. Season to taste with salt and pepper and remove from heat.
