Simmer mustard seeds, sugar, honey, and 45ml water, then stir in vinegar and soak for 4 hours.
Blend seeds with bourbon until creamy but grainy, season, and chill.
Whisk flour, eggs, and milk into a smooth batter and chill for at least 1 hour.
Preheat oven to 200°C.
Sear the beef in hot oil until browned, coat with mustard, and roast for 1.5 hours.
Boil potatoes in salted water for 1 minute, drain, and shake to roughen edges.
Fry potatoes in hot lard or dripping until golden-brown.
Begin roasting the potatoes 30 minutes before the beef finishes.
Remove beef from the oven and let it rest for 30 minutes under foil.
Increase oven to 220°C and roast potatoes for 25 more minutes until crisp.
Reduce beef stock by half in the roasting tray to create a thick gravy.
Heat fat in muffin trays for 10 minutes until smoking hot.
Pour batter into muffin trays and bake at 220°C for 20 minutes without opening the door.
Reduce temperature to 190°C and bake for 13 more minutes until risen.
Carve the beef and serve with gravy, mustard, potatoes, and steamed vegetables.