Preheat oven to 190°C and bring beef to room temperature.
Mix mustard powder with a little water and rub the paste over the beef.
Sear the beef in hot fat in a frying pan until brown on all sides and season.
Roast the beef in a tin for 60 to 90 minutes depending on preferred doneness.
Whisk flour, eggs, milk, and salt into a smooth batter and rest for one hour.
Peel, parboil, and drain potatoes, shaking them to fluff the edges.
Remove beef from oven, cover with foil to rest, and increase oven to 200°C.
Coat potatoes in fat, garlic, and thyme, then roast for 30-35 minutes until golden.
Pour 5mm of oil or dripping into a pudding tin and heat in the oven.
Pour the rested batter halfway into the hot wells of the tin.
Bake puddings for 25-30 minutes until risen and golden.
Pour beef roasting juices into a saucepan.
Deglaze the roasting tin with flour and red wine, then simmer in the saucepan for 10 minutes.
Carve the beef into thick slices and serve with the puddings, potatoes, and gravy.