Pulse the herbs and spices in a spice grinder or food processor a few times to lightly crush the fennel seeds and rosemary. No grinder? Place the spices in a zip-top bag and gently crush them with a rolling pin, or use a mortar and pestle. Rub the spice mixture over the entire pork butt.
1 tbsp. Kosher salt, 2 tsp. black pepper, 1 tsp. onion powder, 1 tsp. garlic powder, 2 tsp. fennel seeds, 1 tsp. dried rosemary, 4 # boneless pork butt