Roughly chop both the tomatoes and the onions and add to the large, heavy based pan.

Add the sugar, mustard powder, crushed garlic, salt and red wine vinegar also to the pan.

Place on a medium to high heat, stirring regularly until the mixture comes to a boil.

Reduce the heat and simmer, uncovered, for approximately 45 minutes. Stirring occasionally.

Allow the mixture to cool slightly before pouring into a blender or using a hand blender to puree the ketchup to a fine consistency.

Clean out the large pan.

Sieve the pureed ketchup into the clean pan, ensuring you push the mixture with a spatula and get all the tasty tomato goodness. You should just be left with tiny fragments of tomato skin and seeds.

Bring the ketchup back to a boil and then transfer into warm, dry bottles of jars and seal with airtight tops.

Label your jars or bottles and store in a cool dark place for up to 6 months.