Place ribs, celery, onion, chillies, garlic, and apple juice in a large saucepan and cover with water.
Simmer the mixture gently for 1 to 1.5 hours until meat is tender, skimming off any scum.
Heat ketchup and sugar in a frying pan for 3 minutes until dissolved.
Stir in Worcestershire sauce, paprikas, and vinegar, then simmer for 5 minutes until thickened.
Add bourbon, remove from heat, and refrigerate once cool.
Whisk egg yolks, mustard, and vinegar, then slowly drizzle in oil to create a mayonnaise.
Mix drained celeriac and parsley into the mayonnaise and season with salt and pepper.
Preheat the oven to 240°C.
Transfer poached ribs to a roasting tray and brush generously with barbecue sauce.
Roast for 15 minutes, turning every 5 minutes until sticky and charred.
Serve the ribs on a platter with slaw and extra sauce on the side.