Cook over medium heat until thickened, 5 minutes. Add the remaining ingredients and simmer until the sauce is the texture of ketchup, 5 minutes more. Transfer to a blender and puree until smooth.
Wash the chipotle chillies, remove the hard stems (leave the seeds in) and place them in a bowl. Pour over 150ml/5fl oz just-boiled water, cover with cling film and soak for about 20 minutes.