1Thinly slice the beef sirloin and marinate with soy sauce, sugar, minced garlic, sesame oil, chopped green onion, and black pepper for at least 30 minutes.
2Preheat oven to 200°C (400°F).
3Cook the marinated beef in a skillet over medium-high heat until browned and cooked through. Let cool slightly.
4Roll out the puff pastry sheets and cut into rectangles.
5Place a portion of cooked bulgogi beef onto one half of each pastry rectangle.
6Fold the pastry over the filling and seal the edges with a fork.
7Beat the egg and brush over the tops of the pastries.
8Bake for 18-20 minutes or until golden brown.
9Mix mayonnaise, gochujang, and rice vinegar to make the gochujang mayo.
10Serve the hot pockets warm with gochujang mayo for dipping.