Place all ingredients in a food processor or blender and puree until very smooth.
Transfer the mixture to a small, heavy-bottomed pot and bring to a gentle simmer. Simmer, and to avoid splatters, continually whisk the mixture for 5 minutes, until it is about as thick as tomato ketchup.
Cool to room temperature and place in a tightly sealing jar.
Refrigerate overnight to allow flavours to meld and then serve. Will keep, refrigerated, for up to 2 weeks.