Prepare the vegetables by washing the celery, peeling the carrots, and removing the onion skins.
Using a cutting board and a sharp knife, chop the veggies into evenly sized pieces. The size can range from minced to ½ inch wide, depending on your preference.
To Freeze
To flash freeze, spread the soffritto out on a baking sheet lined with parchment paper. Freeze it for a few hours, then transfer it to a freezer bag or airtight container and immediately return to the freezer.
To freeze in small portions, scoop single servings into a silicone ice cube tray, silicone muffin cups, or small freezer bags. Label and place in the freezer for later use.
To use frozen soffritto, take a serving out of the freezer and place it into a preheated pan with extra virgin olive oil or unsalted butter and cook over medium-low heat. Use as the flavor base of many dishes, such as soups, pasta sauces, roasts, rice dishes, and more.