Soften the chiles. Place the chiles in a heatproof bowl and cover with boiling water. Let stand for 30 minutes.

Toast the spices. While the chiles 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.

Grind the spices. Grind the spices in a mortar and pestle, spice grinder, or coffee grinder.

Drain the chiles. Drain the chiles, reserving the liquid for step 7.

Stem and seed the chiles. Remove and discard the stems and seeds from the chiles. (Wearing gloves is optional but recommended to protect your hands.)

Combine the chiles with spices, garlic, and salt. Combine the chiles, ground spices, garlic, and salt in the bowl of a food processor. (You can also use a mortar and pestle.)

Make a paste. 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 chile soaking liquid until the paste has reached your desired texture.

Taste and adjust seasonings. 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.

Top with olive oil and store. 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.