Melt butter in a Dutch oven. Add the onion, carrots, potato, and celery; cook and stir for 5-7 minutes until vegetables are tender. Stir in flour, salt, and pepper until blended. Gradually whisk in broth and milk. Bring to a boil while stirring. Reduce heat to low, stirring occasionally, and simmer for 20-30 minutes. Stir in chicken, peas, and corn until heated through. Enjoy!