Creamy Chicken & Rice Soup

In a large pot or Dutch oven, melt butter. Add onion, carrots, and celery. Cook, stirring, until vegetables are tender and liquid has evaporated, 6 minutes. Add chicken and cook until golden, 10 minutes, then add thyme and garlic and stir until fragrant, 1 minute. Season generously with salt and pepper. Add flour and whisk until golden, 1 minute. Pour over chicken broth and milk and season with salt and pepper. Add rice and bring to a simmer until rice is tender and chicken is cooked through.