Season diced chicken breasts with salt and pepper. In a large pot, heat olive oil over medium-high heat. Sauté the chicken until browned on all sides. Remove the chicken from the pot and set aside.
In the same pot, add the frozen mirepois vegetables mix. Sauté until the vegetables are softened, about 5 minutes. Add minced garlic and continue sautéing for another minute.
Sprinkle flour over the sautéed vegetables and stir to coat evenly. Cook for 2-3 minutes.
Gradually add chicken broth while stirring continuously to avoid lumps. Once the broth is incorporated, add milk, dried thyme, and dried rosemary. Stir well.
Bring the mixture to a simmer, then reduce the heat to low. Add the sautéed chicken back into the pot. Let it simmer for about 15-20 minutes or until the chicken is cooked through and the soup has thickened slightly.
Stir in the heavy cream and continue to simmer for an additional 5 minutes. Serve hot.
