Prepare the Compound Butter: In a bowl, combine the softened butter, harissa paste, lemon zest, and chopped parsley. Mix until well combined, then season with salt to taste. Transfer the mixture onto a piece of parchment paper and roll it into a log shape. Twist the ends to seal and refrigerate until firm, about 30 minutes.

Toast Spices: In a dry skillet over medium heat, toast the cumin seeds and black peppercorns until fragrant, about 2-3 minutes. Stir frequently to prevent burning. Remove from heat and let cool slightly. Once cooled, crush the spices using a mortar and pestle or a spice grinder until coarsely ground.

Prepare the Steaks: Pat the sirloin steaks dry with paper towels and rub both sides with olive oil. Generously season with salt and then press the toasted cumin and black peppercorn mixture onto both sides of each steak to form a crust.

Cook the Steaks: Preheat a grill or skillet over high heat. Once hot, add the steaks. Cook for 4-5 minutes on each side for medium-rare, or until your desired doneness is reached. Use a meat thermometer for accuracy (130°F for medium-rare).

Rest and Serve: Remove the steaks from the heat and let them rest for 5 minutes to allow the juices to redistribute. Slice the compound butter into rounds and place on top of the warm steaks. Serve with your choice of sides and enjoy!