1. Combine allspice, cloves, red pepper flakes and mustard seeds in a piece of cheesecloth. Tie securely with a length of kitchen string (to form a spice bag).
2. Bring a large saucepan of water to a boil; place tomatoes in the water and cook until the skins split, 1 to 2 minutes. Then plunge them into a bowl of cold water to stop the cooking. Pat the tomatoes dry, peel them, cut into 1/4-inch pieces.
3. Place the tomatoes and all the remaining ingredients in a heavy saucepan. Add the spice bag and slowly bring the mixture to a boil. Then reduce the heat and simmer for 30 minutes, stirring frequently.
4. NOTE: If using regular tomatoes you may need to simmer additional time and/or thicken somewhat with 1 to 2 teaspoons cornstarch.
5. Remove the pan from the heat and discard the spice bag. Let the jam cool, refrigerate. Makes 1-1/4 cups.