Add to skillet and sauté in oil on medium heat until the onion is translucent.
Add to your soup, entree, etc.
Notes
Do not overcook the veggies! Again the goal is to sweat them, not brown them. Do not use more than medium heat and stir constantly.
Be mindful of the ratio. We used equal parts of the three ingredients, but the standard French technique is 2:1:1 – 2 onions, 1 celery, and 1 carrot. It would always depend on your preference or the recipe you are making.
As the carrots simmer, they get sweeter. If you’re using an extra-large carrot, you might want to use only one or half to avoid overpowering your dish with its flavor.
When making a bigger batch, the pot should be wide with relatively high edges, so the vegetables are easy to stir, eliminating the risk of burning the Mirepoix.
Add the vegetables in the correct order. Diced carrots should come first as they are the toughest of the veggies, followed by onion, and lastly, the celery.
An alternative is adding tomato paste or puree to amp your Mirepoix, especially for brown sauces or gravies. This is called pinçage.