Preheat the oven to 200C Fan.
Season the chicken generously with Maldon salt and leave to sit for 5 minutes.
Add a little oil to an oven-proof frying pan and set over a medium heat. Once hot, add the chicken skin-side down and leave to cook for 5 minutes.
Turn the chicken over and pop in the oven for 10 minutes - or until cooked through and no pink remains inside. (If using skinless chicken, cook for 2 minutes skin-side down, flip it over, and pop in the oven for 10 minutes - or until cooked through and no pink remains inside). Remove from the oven and leave to rest for 5 minutes.
Meanwhile, prepare your stock: mix together the butter and cornflour to form a paste. Stir in the fish sauce. Heat 400 ml of the stock in a medium-sized saucepan over a gentle heat and add 1 tbsp of the butter-cornflour paste to make it lovely and rich.
Next, make the chilli katsu sauce: mix together the sriracha, sweet chilli sauce, paprika and malt vinegar until combined. Add a little to your broth and taste. Gradually add a little more until you are happy with the flavour - remember to go slow and steady, you can always add but you can’t take away!
Add the sliced pak choi and beansprouts and continue to simmer for a few minutes - until al dente.
Meanwhile, cook the noodles according to packet instructions. Drain well and place in a bowl.
Pour the broth over the top, then top with the red onion, spring onion, coriander and chilli.
Slice the rested chicken and gently place on top. Garnish with a wedge of lime and serve.