Food processor or mortar and pestle for mixing paste
1. Place the chilies in a heatproof bowl and cover with boiling water. Let stand for 30 minutes.
2. While the chilies are soaking, toast the caraway, coriander and cumin in a dry skillet over low-medium heat, occasionally shaking or stirring to prevent burning. When the spices are fragrant, remove them from the pan.
3. Grind the spices in a mortar and pestle, spice grinder or coffee grinder.
4. Drain the chilies, reserving the liquid for step 7.
5. Remove and discard the stems and seeds from the chilies. (Wearing gloves is optional but recommended to protect your hands.)
6. Combine the chilies, ground spices, garlic, and salt in the bowl of a food processor. (You can also use a mortar and pestle.)
7. With the food processor running, slowly drizzle in the olive oil and process to form a smooth and thick paste. Scrape down the sides of the bowl occasionally. If a thinner paste is desired, blend in a little of the chili soaking liquid until the paste has reached your desired texture.
8. The flavor of the harissa will deepen over the next day or two, but you can taste it now and add more salt or other optional ingredients to your liking.
9. Transfer the harissa to a jar and cover the surface with a thin layer of olive oil. Cover the jar and refrigerate for up to a month, adding a fresh layer of olive oil on the top each time you use the harissa.
Chilies: Use any chilies you like and have on hand, either a single kind or a combination. For moderately spicy harissa, try a mix of guajillo and New Mexico chilies. Add heat with arbol or puya chilies. Add smokiness with chipotle or morita chilies. Add richness with ancho, mulato, or pasilla chilies. For a very mild harissa, use roasted red bell peppers.
To substitute fresh chilies: Use twice as many fresh as dried (e.g., 8 ounces total fresh instead of 4 ounces total dried). You can also use a mix of fresh and dried chilies.
(Anjali Prasertong is a writer for TheKitchn.com, a nationally known blog for people who love food and home cooking. Submit any comments or questions to firstname.lastname@example.org.)