Pat the beef cheeks dry with paper towels and season them with salt and black pepper on both sides.

In a large heavy-bottomed pot or Dutch oven, heat the olive oil over medium-high heat. Add the beef cheeks to the pot and sear them for about 5 minutes on each side until they are nicely browned. Remove the beef cheeks from the pot and set them aside.

In the same pot, add the chopped onions and cook until they become translucent, about 5 minutes. Stir in the minced garlic and sliced ginger, cooking for an additional 2 minutes until fragrant.

Add the star anise, soy sauce, fish sauce, brown sugar, and beef broth to the pot. Stir well to combine.

Return the seared beef cheeks to the pot, ensuring they are submerged in the liquid. Bring the mixture to a gentle simmer. Cover the pot with a lid and reduce the heat to low. Let the beef cheeks braise slowly for about 3 hours, or until they are tender and easily shred with a fork.

Once the beef is tender, remove the cheeks from the pot and set aside. Strain the liquid to remove the solids, then return the liquid to the pot and simmer for an additional 10-15 minutes until it thickens slightly.

Slice the beef cheeks and arrange them on a serving platter. Pour the silky bone broth gravy over the beef. Garnish with chopped green onions and a sprinkle of sesame seeds before serving.