Add the oil to a pan over a moderate heat; once warm add garlic, cayenne, paprika and chilli flakes, cook for 3 to 5 minutes. Add onion, pepper and chilli cook for 10 minutes. Add chopped tomatoes and puree and cook for a further 10 to 15 minutes. Remove from heat allow to cool then blitz with a hand blender until smooth. Pop in a container and put in fridge, suitable for freezing.