I highly recommend making your own as some shop bought varieties can be quite one-dimensional.You will certainly taste the difference as you noticeable taste the spices and the chillies.
250g long fresh red chillies
3 heaped teaspoons coarsely ground caraway seeds
3 heaped teaspoons coarsely ground cumin seeds
1 level teaspoon ground black cumin seeds (optional)
4 garlic cloves
1 large red bell pepper, roasted, peeled and seeded
1 dessertspoon tomato puree
1 dessertspoon red wine vinegar
2 level teaspoon sweet smoked paprika
6 Tablespoons extra virgin olive oil
sea salt and black pepper
It is advisable to wear rubber gloves when preparing the chillies. Slice the chillies in half lenthways. Lay each chilli on a chopping board cut-side up, gently scrape away the seeds with a teaspoon and discard them. Roughly chop the chillies and transfer to a food processor with a sharp blade. Blend the chillies with a pinch of salt, half of each of the spices and the garlic cloves until as smooth as possible. Transfer to a mixing bowl. Now add the remaining ingredients - the rest of the spices, the peppers, tomato puree, vinegar, paprika and olive oil. Taste and season with more salt to balance out the vinegar.
Harissa keeps well in the fridge, but be sure to cover it with a little oil to seal it from the air.