Simmer tomatoes, onions, and peppers until very soft. Pass through coarse sieve; return purée to pot with sugar, vinegar, and spice bag.
Simmer gently 10–20 minutes, stirring often, until thickened and flavours blended.
Remove spice bag; season with salt and optional paprika. Bottle hot into sterilised jars/bottles. Refrigerate (keeps 1 month) or process for longer storage.