Skin, deseed and roughly chop your tomatoes.
Roughly slice your chillies - deseed them if you want less heat in the sauce.
Add the tomatoes and chillies to a large saucepan along with half the cider vinegar.
Place on a medium heat and bring to a simmer.
Simmer with a lid on for 30 minutes until soft.
Remove your pan from the heat and whizz together - I use a stick/hand blender. Be careful, the mixture is hot and you certainly don't want chilli in your eyes !
Add the sugar and salt to your blended ingredients and place back on the heat. Give the pan's contents a good stir before adding the spice bag.
Leave to simmer uncovered for 30 minutes.
Add the remaining vinegar and simmer for between 30 minutes to one hour until the mixture has reduced down to a nice thick sauce.
Pour into hot sterilised bottles or jars using a funnel.
Heat process by placing bottles into a large saucepan or boiling water canner filled with enough water so that bottles are ¾ covered. Bring water up to boiling point and simmer for 15 mins.