01 -  Preheat oven to 390°F and grease a medium baking dish. 
 02 -  Boil macaroni in a large pot of salted water until just al dente. Drain and set aside. 
 03 -  Melt butter in a medium saucepan over medium heat. Whisk in flour and cook, stirring frequently, for 1 minute until lightly golden. 
 04 -  Gradually whisk in whole milk, stirring constantly until the mixture becomes smooth and thickened, about 4–5 minutes. 
 05 -  Reduce heat to low. Add cheddar, mozzarella, and cream cheese, stirring until all cheeses are fully melted and sauce is creamy. 
 06 -  Mix in gochujang, Dijon mustard, smoked paprika, and ground black pepper. Adjust seasoning with salt to taste. 
 07 -  Fold in chopped kimchi, kimchi juice, and spring onions until evenly distributed. 
 08 -  Add drained macaroni to the sauce and gently mix until every piece is well coated. Transfer to the prepared baking dish. 
 09 -  In a mixing bowl, combine panko breadcrumbs, toasted sesame seeds, melted butter, and sesame oil. Toss until evenly incorporated. 
 10 -  Sprinkle topping evenly over macaroni. Bake for 15–20 minutes until golden brown and bubbling. Allow to cool slightly before serving.