01 - Preheat oven to 400°F. Lightly grease a medium baking dish with butter or cooking spray.
02 - Cook macaroni according to package instructions until al dente. Drain thoroughly and set aside.
03 - In a saucepan over medium heat, melt 2 tbsp butter. Whisk in flour and cook for 1 minute, stirring constantly to form a smooth paste.
04 - Gradually pour in milk while whisking continuously. Continue whisking for 4-5 minutes until sauce thickens and coats the back of a spoon.
05 - Reduce heat to low. Stir in cheddar, mozzarella, Dijon mustard, black pepper, and salt. Mix until cheese is completely melted and sauce is smooth.
06 - Fold cooked macaroni into cheese sauce. Add chopped kimchi, kimchi juice, spring onions, and gochujang. Mix until evenly distributed.
07 - Pour the mac and cheese mixture into the prepared baking dish, spreading evenly.
08 - In a small bowl, combine panko breadcrumbs with 1 tbsp melted butter and sesame seeds. Mix until breadcrumbs are evenly coated.
09 - Sprinkle the breadcrumb mixture evenly over the macaroni surface.
10 - Bake for 15 minutes until the top is golden brown and the sauce is bubbling around the edges.
11 - Let the dish rest for 5 minutes before serving to allow the sauce to set.