1. Peel tomatoes by pricking several times with a sharp knife. Place a few tomatoes into a bowl and cover with boiling water. Stand for 30 seconds. Drain and remove skins. Repeat with remaining tomatoes.
2. Roughly chop tomatoes.
3. Mix chopped tomatoes, chopped onions and salt in a bowl. Cover and stand overnight.
4. Drain off liquid. Place into a saucepan with vinegar and spices. Stir over medium heat until mixture boils.
5. Reduce heat and simmer uncovered for approximately 40 minutes or until mixture is thick, stirring frequently.