Prepare the Compound Butter: In a mixing bowl, combine the softened butter, crushed smoked peppercorns, balsamic vinegar, and fresh thyme leaves. Mix well until all ingredients are fully incorporated. Shape the butter mixture into a log using plastic wrap. Twist the ends to seal and refrigerate until firm, about 30 minutes.

Sear the Sirloin: Preheat your grill or a cast-iron skillet over medium-high heat. Season both sides of the sirloin steaks with salt and black pepper. Add olive oil to the pan or brush it on the grill grates. Place the steaks in the skillet or on the grill. Sear for about 4-5 minutes on each side for medium-rare, adjusting the time for your preferred doneness. Remove the steaks from heat and let them rest.

Cook the Pearl Onions: In the same skillet, lower the heat to medium and add the pearl onions. Sauté for about 5-7 minutes until they are golden brown and soft. Add the chopped thyme and sauté for an additional 2 minutes until fragrant.

Serve: Slice the rested sirloin steaks and plate them. Top with the sautéed pearl onions. Remove the compound butter from the refrigerator and slice into rounds. Place a slice on top of each sirloin steak, allowing it to melt over the warm meat.