• Preheat oven to 400°F/200°C.

Make the Yorkshire pudding batter:

• To a large bow add the flour and salt. Whisk and slowly drizzle in the milk until there are no lumps. Whisk in the egg. Refrigerate for 30 minutes.

Make the beef:

• Coat the beef well with the oil. Sprinkle the salt, pepper and rosemary evenly all over.
• Heat a cast iron skillet or oven-proof skillet on the stove top over medium high heat. Sear the beef on all sides. Transfer the beef in the pan or to a roasting dish and place in the oven. Roast the beef 15 minutes per pound for rare and 20 per pound for medium. ** see note

Make the potatoes:

• While the beef roasts. Add the 6 tablespoons oil/lard or beef fat to a high-sided roasting pan. Place in the oven to heat. Add the potatoes to a large pan and cover with water. Bring to a boil and simmer for 3-4 minutes. You are only par-boiling them. Drain the potatoes into a colander and shake them around. This roughs up the edges and makes them crispy when roasted. Carefully remove the roasting pan with oil from the oven and add the potatoes. Sprinkle evenly with the 1/2 teaspoon salt and turn the potatoes to coat well with the oil and in an even layer. Place back into the oven for 40-45 minutes until golden brown. Turning as necessary to brown all over. They are done when a sharp knife inserts easily. Keep warm covered with foil.
• When the beef is done, remove from the roasting pan onto a platter and cover with foil and allow to rest on a cutting board (reserving any fat ) while you make the gravy and Yorkshire pudding.

Make the gravy:

• To a pan over medium heat and melt the butter. Add the onions and cook until they are softened. Whisk in the flour and cook until it starts to turn a golden color. Whisk in the beef broth/stock until the flour is incorporated and there are no lumps. Simmer until thickened, season with salt and pepper to taste. You can strain the gravy if you wish to remove the onions or any lumps of flour that you can't remove. Keep warm.

Make the Yorkshire pudding:

• Turn up the oven to 425°F/220 °C. If you have any fat from roasting the beef add that to the lard or vegetable oil to make up 12 teaspoons fat and add 1 teaspoon to each cup of a clean 12-cup muffin pan. Place on the center rack of the oven to heat for 10 minutes. The oil should start to smoke. When ready, slide the oven rack out and carefully pour the Yorkshire pudding batter in each of the cups about 1/3 full. Slide the pan back into the oven and bake for 15-20 minutes until browned and puffed. Do not open the oven door before they are finished baking, they will deflate. Remove immediately from the oven when they are risen and golden.
• Slice the beef and serve with the potatoes, your vegeables of choice and Yorkshire pudding. Drizzle with gravy and serve.