Start by washing your vegetables thoroughly. Peel the onion and chop it into 1/2-inch pieces. For the carrot, peel the skin and then slice it into 1/2-inch chunks. Finally, chop the celery rib into 1/2-inch pieces as well. The key is to keep the pieces uniform so they cook evenly.
In a large skillet or sauté pan, heat 1 tablespoon of olive oil over medium heat. Allow the oil to warm up for about a minute until it shimmers.
Add the chopped onion to the skillet first. Sauté the onion for about 3-4 minutes, stirring occasionally until it becomes translucent and fragrant.
Once the onion is soft, add the chopped carrot and celery to the skillet. Stir everything together and continue to sauté for an additional 5-7 minutes.
At this point, you can add a pinch of salt and pepper to enhance the flavors. Once the mirepoix is fragrant and tender, it’s ready to be used in your favorite recipes or stored for later.
