How to Make It
In a large saucepan, cover the chiles with water and bring to a boil. Remove from the heat. Top with a bowl to keep the chiles submerged and let stand overnight.
Stem and seed the chiles and transfer to a large bowl. Reserve the soaking liquid.
In a medium skillet, toast the caraway, cumin, coriander and fennel seeds over moderate heat until fragrant. Transfer to a bowl and let cool completely. In a mortar or a spice grinder, lightly crush the seeds.
In a food processor, combine the seeds with the garlic and rose petals and pulse until a coarse paste forms. Add the seeded chiles and 1/2 cup of the reserved soaking liquid to the processor along with the lime juice and rose water. Process until the chiles are very finely chopped, scraping down the side of the bowl as needed. Add 1/4 cup of olive oil and 1 1/2 tablespoons of kosher salt and pulse to combine. Season with additional salt if necessary. Scrape the harissa into jars, cover with a thin layer of olive oil and a lid and refrigerate for up to 2 months.
Organic rose petals are available at amazon.com.