Soak all the dried chili peppers including the chilis de arbol in a pot with warm water for 1 hour. 

Strain the peppers and remove their seeds and stems. Lay the peppers over a paper towel-lined tray and set them aside to dry for about 15 minutes.

Place the peppers and garlic cloves into a food processor. Process the mixture until a smooth paste is formed.

Transfer the pepper and garlic paste into a large mixing bowl. Add the cumin and salt and mix well until combined. Taste to adjust any seasonings.

Transfer the harissa paste into a 1 ½ cup sterile glass jar. Pour up to ½ cup of olive oil over the paste to seal the harissa.