In Tunisia it would be prepared fresh in a spice shop. The simplest recipe is merely a paste of red chili peppers and salt that is covered in olive oil and stored. Harisa is sold in tubes by both Tunisian and French firms. The Tunisian one is better but neither can compare to your own freshly made from this recipe. I first became intrigued with making harisa from a preparation made by Mouldi Hadiji my Arabic teacher of twenty years ago.
Some cooks also use mint, onions, or olive oil in their harisa.
I modified the recipe after much consultation with an illustrious group of opinionated people, including Chef Moncef Meddeb, Mohammed Kouki, the doyen of Tunisian food experts, and cookbook authors Paula Wolfert, Kitty Morse, Nancy Harmon Jenkins, and Deborah Madison. Be very careful when handling hot chili peppers, making sure that you do not put your fingers near your eyes, nose, or mouth, or you will live to regret it. Wash your hands well with soap and water after handling chili peppers. After you make your first harisa, with all the modern conveniences, I hope you can appreciate what exacting women's work this was, making it in the traditional mortar. Drain and remove the stems and seeds.