Heat the butter and oil in a medium pot with a tight fitting lid over medium heat. Once its melted and hot, add the carrots, celery and onion with a large pinch of salt. Cook, stirring often, until everything has softened up...about 7-10 minutes. Then add the garlic and cook a minute or two more, until fragrant. Stir in the rice and seasonings and increase the heat to med-high.