01 - Preheat oven to 390°F (200°C). Lightly grease a medium baking dish.
02 - Boil elbow macaroni in salted water until al dente. Drain thoroughly and set aside.
03 - In a medium saucepan over medium heat, melt butter, add flour, and whisk for 1 minute.
04 - Gradually pour in milk while whisking until mixture is smooth and thickened, about 4–5 minutes.
05 - On low heat, stir in cheddar, mozzarella, and cream cheese until thoroughly melted.
06 - Blend gochujang, Dijon mustard, smoked paprika, and black pepper into the sauce. Adjust salt to taste.
07 - Gently fold in chopped kimchi, kimchi juice, and spring onions until evenly distributed.
08 - Stir drained macaroni into the cheese sauce, ensuring all pasta is fully coated. Transfer to prepared baking dish.
09 - Mix panko, toasted sesame seeds, melted butter, and sesame oil in a bowl. Sprinkle topping evenly over the macaroni.
10 - Bake in preheated oven for 15–20 minutes until golden brown and bubbling. Let cool for several minutes before serving.