Let beef reach room temperature, score the fat, and rub with oil and salt.
Preheat oven to 220°C.
Fry onions in 50g butter until tender.
Mix breadcrumbs, mustard, water, 3 eggs, and seasoning into a paste.
Spread paste over beef and cover with greased foil.
Place beef on top of carrots in a tray with a little water.
Place in oven and immediately reduce heat to 200°C.
Roast for two hours, remove foil, and roast for one more hour.
Rest meat for 20 minutes.
Whisk 8 eggs with 600ml milk and salt, then beat in 500g sifted flour.
Heat dripping in a pudding tin at 200°C until smoking.
Ladle batter into the tin and bake for 15 minutes.
Carve the beef and serve with puddings, carrots, and gravy.