Throw all the ingredients in a small sauce pan and heat. Leave to simmer for 10 minutes.
Once simmered, cool slightly and then blend in a blender until smooth. Serve straight away or cool and store in the fridge until ready to eat.
Tomato sauce - in case anyone wondered, I mean ketchup, as in the condiment itself (not a tin of tomatoes). Use ketchup (any will do).Onion powder - you can buy it online if you can't find it in supermarkets. We got ours from Costco but they also sell it at Wholefoods Online. Storage - store in the fridge in a Tupperware/glass/jar - whatever takes your fancy! Seal it well and it'll keep for a couple of weeks (or more). I expect you can keep it longer but I've only ever kept mine for two weeks.