A combination of carrots, celery, and onion used in most culinary dishes as a base. Although mirepoix is rarely kept in the final dish, it adds depth to the flavor as well as a brown coloring. For white mirepoix, simply substitute mushrooms, more onions, or even leeks in place of carrots. Mirepoix is always created with a two-parts carrot to one part onion and one part celery combination.
Maybe a bit of mirepoix would add a bit of flavor to that dull jus.