Cook the onions, carrots, and celery in the oil for 3 minutes, stir often. Add the garlic, Italian seasoning, salt, and pepper to the pot and cook for 1 minute, stirring often.
Melt the butter. Add the flour. Cook the mixture for 1-2 minutes. Stir often. Slowly add in the chicken broth. Stir until the flour mixture dissolves in the broth.