01 - Preheat oven to 390°F (200°C) and grease a medium baking dish.
02 - Boil elbow macaroni in salted water until just al dente, then drain and set aside.
03 - In a medium saucepan over medium heat, melt butter. Whisk in flour and cook for 1 minute.
04 - Gradually add milk, whisking continuously until the sauce is smooth and thickened, about 4–5 minutes.
05 - Reduce heat and add cheddar, mozzarella, and cream cheese, stirring until fully melted.
06 - Mix in gochujang, Dijon mustard, smoked paprika, and black pepper. Adjust salt to taste.
07 - Fold in chopped kimchi, kimchi juice, and spring onions.
08 - Add drained macaroni to the cheese sauce and mix until evenly coated. Transfer mixture to the prepared baking dish.
09 - In a bowl, combine panko breadcrumbs, toasted sesame seeds, melted butter, and sesame oil. Sprinkle topping evenly over pasta.
10 - Bake for 15–20 minutes until the top is golden and bubbling. Cool slightly before serving.