Pat beef cubes dry using paper towels to ensure a good sear and season lightly with salt and black pepper.
In a bowl, mix soy sauce, Worcestershire sauce, oyster sauce, brown sugar, and chili flakes until well combined.
Heat olive oil in a hot pan over medium heat and fry garlic until golden brown and crispy, then set aside.
Increase heat to medium-high and let the pan get very hot before adding beef.
Sear beef cubes in a single layer for 1½–2 minutes per side until browned and slightly caramelized.
Pour in the prepared sauce and toss quickly until it starts bubbling and coats the beef evenly.
Lower heat and add butter, stirring until it melts and forms a glossy sauce.
Return fried garlic to the pan and mix gently for extra flavor and aroma.
Remove from heat and garnish with chopped scallions before serving hot.