Soak the dried chillis in warm water until they become pliable. Drain and discard the soaking water. Set the chillis aside.
Toast the caraway, coriander, cumin and fennel seeds until they are fragrant. Set aside.
Remove the tough bottom from the garlic cloves, crush and peel.
In a mortar and pestle, or a food processor, crush the toasted spices and the cloves until finely ground. Add the garlic and salt, and reduce to a paste. Add the rehydrated chillis, one by one, and crush. You may need to remove some of the paste as you go go along to make room in the mortar. Add some olive oil to help with the grinding process, if needed.
Mix all remaining ingredients together. The final product should be a rough paste.
In an airtight jar, harissa paste should keep for a few weeks in the refrigerator. Just make sure the paste's surface is covered with oil at all times.
To vary the flavour of your harissa, add some preserved lemon peels or even substitute the lemony brine for salt. Or for a Tunisian accent, add some walnuts to the mix.
«Harissa has lovely, complex flavours, and is a great alternative to searing hot chilli sauces.»