In a large soup pot or Dutch oven, melt 1 tablespoon of butter over medium heat. Add the diced chicken and cook until lightly browned. Remove the chicken and set aside.

Add the remaining butter to the pot. Once melted, add the onion, carrot, celery, and garlic. Cook, stirring occasionally, until the vegetables are softened.

Stir in the flour and cook for 1–2 minutes, stirring constantly. Slowly whisk in the chicken broth until smooth and no lumps remain.

Add the diced potatoes and bring the soup to a simmer. Cook for 15–20 minutes, or until the potatoes are tender and easily pierced with a fork.

Return the chicken to the pot, then stir in the peas, corn, celery seed, and thyme. Let everything heat through.

Reduce the heat to low and stir in the heavy cream. Taste the soup and season with salt and pepper as needed.

Serve warm, topped with fresh parsley if desired.