Buffalo chicken burgers

Name: Buffalo chicken burgers
Ingredients: 30g/1oz butter; 4 tbsp chilli sauce; 1½ tsp white wine vinegar; 2 tsp Worcestershire sauce; pinch each of celery salt, cayenne pepper and black pepper; ½ tbsp barbecue sauce; 2 drops smoke oil (optional); 50ml/2fl oz buttermilk; ½ small red cabbage, shredded or grated; ½ carrot, grated; ½ red onion, thinly sliced; ½ red chilli, finely chopped; 1 tbsp finely chopped coriander leaves; 1–2 heaped tbsp mayonnaise; 50g/1¾oz panko breadcrumbs; 1½ tsp ground coriander; 1½ tsp ground fennel seeds; 50g/1¾oz plain flour; 1 free-range egg, lightly beaten; 2 chicken breasts (approximately 175g/6oz), butterflied; 1 tbsp sunflower oil; 4 pretzel buns, or similar, cut in half and toasted, to serve