Preheat the oven to 400°F (200°C). Cut the top off the head of garlic to expose the cloves. Drizzle with olive oil, wrap in foil, and roast for 30-35 minutes until soft and caramelized. Allow to cool, then squeeze the roasted garlic cloves into a bowl.

In the bowl with the roasted garlic, add the softened butter and chopped parsley. Use a fork or a hand mixer to whip until well combined and creamy. Season with salt to taste. Set aside.

Pat the flank steak dry with paper towels. Season both sides with salt and blackening seasoning. In a large skillet, heat the olive oil over medium-high heat until shimmering. Add the seasoned flank steak to the skillet and sear for 4-5 minutes on each side for medium-rare, or until your desired doneness is reached.

In the last minute of cooking, sprinkle the chopped scallions and sesame seeds over the steak. Flip the steak to toast the sesame seeds slightly and allow the scallions to wilt.

Remove the skillet from the heat and transfer the steak to a cutting board. Let it rest for 5-10 minutes before slicing against the grain.

Serve the sliced flank steak with a generous dollop of whipped roasted garlic butter on top.