Preheat the oven to 300°F (150 degrees C). Tear sourdough bread into rough pieces and place it in a food processor along with fresh rosemary leaves and fresh basil leaves.
Process into crumbs.
Transfer the crumbs to a large mixing bowl. Add minced garlic, salt, and lack pepper powder to the bowl and massage together for a minute with your hands, until thoroughly combined.
Drizzle extra virgin olive oil and salted butter over the breadcrumbs and continue massaging from the bottom to the top for another minute.
Transfer the mixture to a high-walled oven-safe dish, like a Pyrex or deep cake pan, and spread evenly.
Place in the middle rack of the preheated oven for 35-40 minutes, stirring every 15 minutes, until the breadcrumbs are golden brown and fragrant. Once done, remove the tray from the oven and let the pangrattato cool at room temperature.