Peel and mince the garlic. Grate the ginger. Thinly slice the green onions and finely dice the onion. Toast the sesame seeds in a dry skillet for 1–2 minutes until fragrant; set aside.

Make marinade

In a bowl, combine soy sauce, brown sugar, mirin, sesame oil, minced garlic, grated ginger, gochujang (if using), and black pepper. Whisk until sugar dissolves.

Marinate and cook filling

Heat 1 tablespoon vegetable oil in a skillet over medium-high heat. Add the diced onion and cook 2–3 minutes until translucent. Add the ground pork (and finely chopped sliced beef if using) and cook, breaking up lumps, until no longer pink, about 5–6 minutes. Pour the marinade over the meat, stir to coat, and simmer 2–3 minutes until slightly reduced. Stir in the sliced green onion and toasted sesame seeds. Taste and adjust seasoning (add a pinch more sugar or soy if needed). Remove from heat and let cool to room temperature (10–15 minutes).

Pastry & Assembly

Preheat & prepare pastry

Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper. Lightly dust a clean work surface with a teaspoon of flour. Unfold puff pastry sheets and roll lightly with a rolling pin to smooth seams and enlarge to roughly 10x12 inches each (work quickly to keep pastry cold).

Assemble sausage rolls

If sausages are raw, cook them according to package instructions and cool. Place one sausage near the short edge of a pastry sheet. Spoon a generous strip (about 2–3 tablespoons) of the cooled bulgogi filling along the length of the sausage, pressing slightly so the filling adheres. Fold the pastry over the sausage and filling, sealing the long edge by pinching or brushing with a little egg wash (beat egg with 1 tsp water). Trim excess pastry if needed and tuck ends under. Repeat so you have 6 rolls across the two sheets (depending on sheet size, you may cut each sheet into 3 rectangles). Use toothpicks to secure seams if desired.

Egg wash & scoring

Place assembled rolls seam-side down on prepared sheet. Brush tops evenly with egg wash. Lightly score the tops with a knife 2–3 times to allow steam to escape and create a decorative pattern. Sprinkle a few extra toasted sesame seeds over the tops if desired.

Bake

Bake in preheated oven for 18–22 minutes, rotating the sheet halfway through, until pastry is puffed and deep golden brown. If bottoms are browning too fast, move sheet to a higher rack or place on an additional baking sheet.

Finish

Remove from oven and let cool 5 minutes on the sheet, then transfer to a wire rack. Remove any toothpicks before serving.

Optional Dipping Sauce

Whisk together mayonnaise, gochujang, lime juice (or rice vinegar), honey, and sesame oil in a small bowl until smooth. Taste and adjust seasoning. Serve alongside warm sausage rolls.