Heat the olive oil in a heavy saucepan over medium-high heat.
2 teaspoons olive oil
Once the oil is hot, add the celery, onion, and carrots. Cook, stirring frequently, until the onions are just beginning to caramelize, about 10 minutes.
1 cup celery, 1 cup onion, 1 cup carrots
Add the wine and cook until the sauce is reduced by half, about 5 minutes or so.
1 cup dry red wine
Add the stock and tomato paste, then mix until well-combined.
4 cups unsalted or low-sodium beef stock, 2 tablespoons tomato paste
Decrease the heat to medium-low and simmer until the sauce decreases in volume by one-quarter, about 25 minutes.
Remove the sauce from heat, allow it to cool, and then strain it into a measuring jar or container.