Heat a deep pan one-third full of vegetable oil until a breadcrumb sizzles.
Mix 50g butter with chilli, garlic, parsley, and lemon juice in a bowl.
Split the chicken breast horizontally and flatten between greaseproof paper using a mallet.
Place the butter mixture inside the chicken and fold the meat to wrap it completely.
Coat the chicken in seasoned flour, then egg, then breadcrumbs, repeating the egg and crumbs once.
Deep-fry the kiev in hot oil for 10 minutes and drain on towels.
Boil the chopped potato until tender and drain.
Mash the potato with 50g butter, cream, chives, and cheese, then season with salt and pepper.
Serve the kiev sliced open on a warm plate with the herb mash.