01 - Preheat oven to 400°F and lightly grease a medium baking dish
02 - Cook macaroni according to package instructions until al dente, then drain and set aside
03 - Melt 2 tbsp butter in a saucepan over medium heat, whisk in flour, and cook for 1 minute
04 - Gradually whisk in milk, stirring constantly until smooth and thickened, about 4-5 minutes
05 - Reduce heat to low and stir in cheddar, mozzarella, mustard, pepper, and salt until melted and smooth
06 - Fold in cooked macaroni, chopped kimchi, kimchi juice, spring onions, and gochujang until well mixed
07 - Pour the mixture into the prepared baking dish
08 - Combine panko breadcrumbs with melted butter and sesame seeds, then sprinkle evenly over the macaroni
09 - Bake for 15 minutes until golden and bubbling
10 - Let rest for 5 minutes before serving