In a saucepan or saucepan with a thick bottom, heat the oil, add finely chopped onions and cook for 8-10 minutes until it becomes transparent. When the onion softens add mashed tomatoes, crushed garlic and spices, salt and pepper to taste. Stir. Loosely cover and cook on low heat for at least 30 minutes, stirring occasionally and adding the drained tomato juice if the sauce will thicken strongly. This sauce can be prepared in advance and stored in the refrigerator or freeze.