Homemade Tomato Sauce

Combine the oil and onion in a large pot and cook over moderate heat until the onion starts to brown, about 10 minutes, stirring frequently. Add the garlic, rosemary, and celery and cook another 5-8 minutes, or until the celery is soft.

Stir in the tomatoes and bring to a boil, stirring frequently. Lower the heat to a simmer, set the lid at an angle, and cook until the sauce is thick, about 30 minutes. Season with salt and pepper. This sauce will keep in the refrigerator for up to 1 week, or in the freezer up to 6 months.

Makes 4 cups